Photovoltaic power generation-battery energy storage converter with reconfigurable function

Abstract

The invention belongs to the technical field of converter control, and discloses a photovoltaic power generation-battery energy storage converter with a reconfigurable function, which comprises eight switching tubes and a coupling inductor. The design of the cascaded double H bridges enables the sub-modules to flexibly work in series, parallel, boost or bypass modes, the'short plate effect 'caused by connection aging, local shadow or defects and the like of a traditional long photovoltaic string is improved, all energy conversion links of the method are integrated in one converter, and the loss during energy conversion is reduced. The invention further discloses a control method of the converter, load constant-voltage control and photovoltaic array maximum power tracking control are decoupled according to the overall thought, the harmonic component output by a system is reduced through a multi-level control strategy, and the electric energy quality is improved; the coupling inductors are additionally arranged among the modules, so that the maximum power tracking of each photovoltaic array can be realized without the aid of a traditional boost circuit, the power generation efficiency of the system is improved, and the battery pack can effectively realize power balance.

Description

Technical Field

[0001] The present invention belongs to the technical field of converter control, and in particular relates to a photovoltaic power generation-battery energy storage converter with a reconfigurable function and a control method thereof. Background Art

[0002] Traditional photovoltaic power generation and battery energy storage systems are interconnected by a common AC bus after DC / DC converters and DC / AC converters, respectively. When the system becomes larger and more complex, the design of topologies like this faces challenges because the series hard-connected parts of the system are vulnerable to the "short board effect", that is, the weakest component, such as a defective, shaded photovoltaic module or an aging battery, will limit the performance of the system. Therefore, series systems with hard connections usually have load sharing problems and problems caused by partial shading. In addition, the lack of flexibility of hard-wired series connections reduces overall efficiency and reliability. It is of great significance to develop a flexible and dynamically variable converter, which can not only alleviate the "short board effect" of the system, but also allow photovoltaic modules to always operate at their respective maximum power points under different weather and temperature conditions.

[0003] On the other hand, in traditional photovoltaic power generation and battery energy storage systems, each unit has its own inverter and is connected in parallel on the grid side. Three conversion steps are required for the excess energy that is transferred from the photovoltaic system to the energy storage unit at a certain point in time and from the energy storage unit to the grid at another point in time. This topology has obvious disadvantages, such as the limited pump-up voltage range of the first-stage DC / DC boost converter and the large AC harmonic components of the DC / AC converters mostly implemented by VSC in the second stage. Summary of the invention

[0004] In view of this, the present invention proposes a photovoltaic power generation-battery energy storage converter with reconfigurable function and a control method thereof. All energy conversion links are concentrated in one converter and have flexible variable structure characteristics to ensure that each photovoltaic unit operates at its respective maximum power point. The system also has a load sharing function, thereby improving the energy conversion efficiency and the stability of the system.

[0005] The present invention provides a converter with a reconfigurable function, wherein the reconfigurable converter connects a photovoltaic array and a battery pack, that is, each battery pack is located between two PV arrays, forming a PV-BT-PV dedicated module cluster, and according to the system output voltage level and power size, a bus system with a single module cluster (1) or even multiple module clusters (k) interconnected is formed, and the MMC control strategy is used to achieve high-quality power output and jointly supply power to the load. The converter is responsible for coordinating the energy flow between the load and the two energy sources.

[0006] The present invention takes a single module cluster (the first one) as an example to illustrate the hardware architecture of the system, but it is not limited to one. Systems with multiple module clusters will also fall within the scope of protection of the present invention. In the first module cluster, it includes: Photovoltaic array PV 1 Unit, battery pack BT 1 Unit, photovoltaic array PV 2 Unit and converter unit; The converter units are four in total, namely: converter CON 0 、Converter CON 1 、Converter CON 2 and converter CON 3 ; The following is the converter CON 1 As an example, eight power switch tubes form a cascaded double H-bridge structure, including: power switch tube S 11 , S 12 , S 13 , S 14 , S 15 , S 16 , S 17 , S 18 , coupled inductor L 1 ; Switching tube S 11 The drain of the switch tube S 13 The source electrode of forms the first bridge arm; Switching tube S 12 The drain of the switch tube S 14 The source electrode forms the second bridge arm; Switching tube S 15 The drain of the switch tube S 17 The source of forms the third bridge arm; Switching tube S 16 The drain of the switch tube S 18 The source of forms the fourth bridge arm; Switching tube S 11 The source and switch tube S 12 The source of the short circuit is connected to the photovoltaic array PV 1 The positive terminal of the cell; Switching tube S 13 The drain and switch tube S 14 The drain of the PV array is short-circuited and connected to the 1 The negative terminal of the cell; Switching tube S 15 The source and switch tube S 16 The source of the short circuit, connect the battery pack BT 1 The positive terminal of the cell; Switching tube S17 The drain and switch tube S 18 The drain of the battery pack is short-circuited and connected to the BT 1 The negative terminal of the cell; Coupled inductor L 1 Two terminals of a coil are connected to the midpoints of the first bridge arm and the second bridge arm respectively; Coupled inductor L 1 Two terminals of the other coil are connected to the midpoints of the third bridge arm and the fourth bridge arm respectively.

[0007] Preferably, the switch tubes are all MOS tubes.

[0008] Preferably, the converter with reconfigurable function provided by the present invention further includes a first control branch, a second control branch, and a modulation unit; the first control branch is used to obtain the terminal voltage of the load and generate a control signal M 0 The second control branch is used to obtain the output voltage and output current of the photovoltaic array and generate a control signal M d The modulation unit is used according to the control signal M 0 and the control signal M d Generate a driving signal for the power switch tube.

[0009] Preferably, in the converter with reconfigurable function provided by the present invention, the modulation unit adopts carrier phase shifting technology to respectively 1 Unit, battery pack BT 1 Unit, photovoltaic array PV 2 The modulation reference of the unit is compared with the triangular carrier signal to obtain the driving signal of the switch tube, and the waveform finally output by the converter is a multi-level step wave. Since the advantage of carrier phase shifting technology is that it can use the SPWM method with low switching frequency, the switching loss and noise can be reduced, and the output voltage quality of the system can be improved, especially when the photovoltaic power generation-battery energy storage system is a high-voltage and high-power application, its advantages are more obvious.

[0010] The present invention also provides a control method for a photovoltaic power generation-battery energy storage converter with a reconfigurable function, which specifically comprises: obtaining the terminal voltage of the load, generating a control signal M 0 , the control signal M 0 Used to achieve the load constant voltage control; obtain the output voltage and output current of the photovoltaic array, and generate a control signal M d , the control signal M d Used to realize the maximum power point tracking control of the photovoltaic array; the photovoltaic array PV 1 Unit, battery pack BT 1 Unit, photovoltaic array PV 2The connection groups of the units vary according to the drive signals of the converter switch tubes, which can be series, parallel, boost mode and bypass mode. The coupled inductor acts as a temporary energy storage or low impedance path between the photovoltaic array unit and the battery pack unit, realizing the decoupling control of the system voltage and power.

[0011] Compared with the prior art, the converter with reconfigurable function proposed in the present invention has the following advantages: the photovoltaic array and the battery pack are in one converter, and the system topology is simplified compared with the traditional DC / DC and DC / AC multi-level converters; the multi-level converter strategy has a small system output harmonic component compared with VSC in high-voltage and high-power applications, and the size and cost of the filter are reduced; the flexible reconfigurable function between units avoids the "short board effect" brought about by the hard connection of the traditional photovoltaic power generation-battery energy storage system, and allows each photovoltaic array unit to work at its maximum power point, thereby improving the power generation efficiency of the system; the bypass mode enables the system to have a fault ride-through function, and in extreme cases of certain units, the system can be kept from shutting down, thereby ensuring the stability of the system operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 Schematic diagram of the circuit topology of a photovoltaic power generation-battery energy storage converter with reconfigurable function according to an embodiment of the present application.

[0013] Figure 2 for Figure 1 Detailed circuit diagram of one working cluster in the reconfigurable converter shown.

[0014] Figure 3 for Figure 1 The control schematic diagram of the reconfigurable converter is shown.

[0015] Figure 4 for Figure 1 The equivalent circuit diagram of the reconfigurable converter shown works in series mode.

[0016] Figure 5 for Figure 1 The equivalent circuit diagram of the reconfigurable converter shown in FIG. 1 is when the converter operates in parallel mode.

[0017] Figure 6 for Figure 1 The equivalent circuit diagram of the reconfigurable converter shown in FIG. 1 is when the converter operates in boost mode.

[0018] Figure 7 for Figure 1 The equivalent circuit diagram of the reconfigurable converter shown in FIG. 1 is when the converter operates in bypass mode.

[0019] Figure 8 (a) Figure 1The output voltage waveform of the reconfigurable converter system when the load changes.

[0020] Figure 8 (b) Figure 1 The output current waveform of the reconfigurable converter system when the load changes.

[0021] Fig. 9 for Figure 1 The maximum power point tracking accuracy waveform of four photovoltaic arrays connected to the reconfigurable converter is shown.

[0022] Fig.10 for Figure 1 The state of charge curve diagram of two battery packs connected to the reconfigurable converter is shown.

[0023] Fig.11 (a) Figure 1 The output voltage waveform of the reconfigurable converter system when the voltage setting changes.

[0024] Fig.11 (b) Figure 1 The output current waveform of the reconfigurable converter system when the voltage given changes. DETAILED DESCRIPTION

[0025] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] like Figure 1 As shown in FIG. 1 , a reconfigurable converter is connected to two PV-BT-PV photovoltaic arrays and a battery module cluster. Figure 2 As shown, each converter is composed of eight power switch tubes and a coupled inductor. The eight switch tubes form a double H bridge, and the inductor is located at the midpoint of the double bridge. In this embodiment, the converter CON 1 Take the following as an example to implement the hardware connection.

[0027] Switching tube S 11 The drain of the switch tube S 13 The source of the switch tube S 12 The drain of the switch tube S 14 The source of the switch tube S 15 The drain of the switch tube S 17 The source of the switch tube S 16 The drain of the switch tube S18 The source of the fourth bridge arm is formed. When controlling, the switching states of the two switch tubes on each bridge arm are required to be complementary. Taking the first bridge arm as an example, when the switch tube S 11 When sending a conduction signal, be sure not to give the switch tube S 13 Send a trigger signal to ensure it is in the off state.

[0028] Switching tube S 11 The source and switch tube S 12 The source of the short circuit is connected to the photovoltaic array PV 1 The positive pole of the unit; the switch tube S 13 The drain and switch tube S 14 The drain of the PV array is short-circuited and connected to the 1 The negative pole of the unit; the switch tube S 15 The source and switch tube S 16 The source of the short circuit, connect the battery pack BT 1 The positive pole of the unit; the switch tube S 17 The drain and switch tube S 18 The drain of the battery pack is short-circuited and connected to the BT 1 The negative terminal of the unit. The coupled inductor L 1 The two terminals of a coil are connected to the midpoints of the first bridge arm and the second bridge arm respectively; the coupling inductor L 1 Two terminals of the other coil are connected to the midpoints of the third bridge arm and the fourth bridge arm respectively.

[0029] According to an exemplary but non-limiting embodiment, in this embodiment, the control circuit controls the on and off of the switch tube, and the control circuit includes a first control branch, a second control branch, and a modulation unit, and the first control branch and the second control branch are connected to the modulation unit; the first control branch is used to obtain the terminal voltage of the load and generate a first control signal to achieve constant voltage control at both ends of the load; the second control branch is used to obtain the output voltage and output current of four photovoltaic arrays and generate a second control signal to achieve maximum power tracking control of the photovoltaic array.

[0030] According to an exemplary but non-limiting embodiment, the modulation unit includes modulation reference calculation of the converter, comparison of the modulation reference signal with the triangular carrier signal, and SPWM triggering of the cascaded double H-bridge converter. The first control branch includes an adder and a PI controller, the negative input end of the adder is connected to the two ends of the load through a voltage sensor, and the positive input end is a preset load voltage reference value; the input end of the PI controller is connected to the output end of the adder, and the output end is connected to the modulation reference calculation of the converter of the modulation unit. The second control branch includes MPPT control and inter-module current calculation, the voltage input end of the MPPT control is connected to the two ends of the four photovoltaic arrays through a voltage sensor, and the current input end is connected to the output end of the four photovoltaic arrays through a current sensor; the output end of the MPPT control is connected to the input end of the inter-module current calculation; the four outputs of the inter-module current calculation are respectively connected to the modulation reference calculation input of the converter of the modulation unit.

[0031] In this embodiment, Figure 3 The system control strategy block diagram is given. The first control branch samples the load terminal voltage V from the output terminal of the load. out The adder calculates the load voltage reference value V according to the preset load voltage reference value V ref And the load voltage sampling value V out Calculate and get the error signal V e , and then obtain the first control signal M through the PI controller 0 The output voltage V of the four photovoltaic arrays in the second control branch pv1 、V pv2 、V pv3 、V pv4 and output current I pv1 ,I pv2 ,I pv3 ,I pv4 The voltage reference of the photovoltaic array is used as the current reference of the inter-module current calculation unit. After the calculation, the second control signal M is obtained. di ,i [1, 2, 3, 4].

[0032] The first control signal M 0 and the second control signal M di The modulation reference calculation of the converter input into the modulation unit is respectively obtained to obtain the modulation signal m i1 / i2 ,i [0, 1, 2, 3, 4, 5], which is expressed as: (1)

[0033] In this embodiment, the modulation unit adopts carrier phase shift technology, and the switch states of the two switch tubes in each bridge arm are complementary. In the positive half cycle of the AC output, the switch state of each switch tube depends on the size of the modulation wave and the carrier, and the logical relationship follows the expression:

[0034] (2)

[0035] (3).

[0036] Here, C i Represents the carrier signal, U i and L i Indicates the switching state of the upper and lower bridge arm switches of the converter, 0 represents off and 1 represents on.

[0037] Similarly, in the negative half cycle of the AC output, the switching state of the upper and lower bridge arm switches of the converter follows the expression:

[0038] (4)

[0039] (5)

[0040] In this embodiment, the converter can work in four different modes, namely, series connection, parallel connection, boost and bypass between modules. 1 Let's take an example to illustrate:

[0041] (1) Series mode (PV array 1 With battery pack BT 1 Combined power supply mode): When the power generated by the photovoltaic array cannot meet the load demand, the photovoltaic array PV in the system 1 With battery pack BT 1 The combined power is used to supply power to the load. 11 With S 12 Shutdown, S 13 With S 14 Conductivity; S 15 With S 16 On, S 17 With S 18 Shut down.

[0042] The equivalent circuit is Figure 4 As shown, L 11 and L 12 Represents coupled inductor L 1 The self-inductance of the two coils, i 11 and i12 are the currents flowing through them, M 12 and M 21 Represents coupled inductor L 1 The mutual inductance between the two coils, i out and i circ are the currents flowing through the load and in the loop respectively. According to Kirchhoff’s current law, we can conclude that:

[0043] (6)

[0044] (7)

[0045] To simplify the analysis, we assume L 11 = L 12 ≈ M 12 = M 21 According to Kirchhoff's voltage law, the voltage in the circuit satisfies the expression:

[0046] (8)

[0047] Substituting expressions (6) and (7) into expression (8), we can obtain:

[0048] (9)

[0049] In order for expression (9) to hold, It must be zero, that is, the current change in the loop is approximately zero. This indicates that the converter works in series mode, and the coupled inductor has almost no effect on the load current, showing a low impedance characteristic.

[0050] (2) Parallel mode (PV array 1 Simultaneously supply BT to the load and battery pack 1 Power supply mode): When the power generated by the photovoltaic array is greater than the power required by the load, the photovoltaic array PV in the system 1 In addition to meeting the load requirements, the power generated will also transfer excess power to the battery pack BT 1 At this time, the switch tube S 11 With S 14 On, S 12 With S 13 Shutdown; S 15 With S 18 Shutdown, S 16 With S17 Conductivity.

[0051] The equivalent circuit is Figure 5 As shown, according to Kirchhoff's voltage law, the voltage in the circuit satisfies the expression:

[0052] (10)

[0053] Transform expression (10) into:

[0054] (11)

[0055] Expression (11) shows that when the converter works in parallel mode, the presence of the coupled inductor has a strong carrying capacity for the voltage difference between modules, especially when the converter works at a high switching frequency, the coupled inductor protects the switch tube well.

[0056] (3) Boost mode (PV array 1 Energy temporary storage mode): When the system has a tendency to make the photovoltaic array work in parallel and the battery pack work in series, the photovoltaic array PV 1 The energy generated can be temporarily stored in the coupled inductor, which is similar to the boost circuit of the traditional DC / DC. 11 With S 14 On, S 12 With S 13 Shutdown; S 15 With S 16 On, S 17 With S 18 The equivalent circuit is as follows Figure 6 shown.

[0057] (4) Bypass mode (PV array 1 Bypass mode): When the system has a tendency to make the photovoltaic array work in series and the battery pack work in parallel, the energy previously temporarily stored in the coupled inductor will be transferred to the battery pack BT 1 Charging, photovoltaic array PV 1 In this transient state, there is no contribution to the circuit, which is called bypass mode. 11 With S 12 Shutdown, S 13 With S 14 Conductivity; S 15 With S 18 Shutdown, S 16 With S 17 The equivalent circuit is as follows Figure 7 shown.

[0058] In order to verify the correctness of the theoretical analysis, the present invention uses MATLAB simulation software to build a set of photovoltaic power generation-battery energy storage converter simulation models with reconfigurable functions, and its design indicators are shown in Table 1.

[0059] Table 1 Parameters of each unit of the photovoltaic power generation-battery energy storage converter with reconfigurable function

[0060]

[0061] The simulation verifies the performance of the system from the following two situations:

[0062] (1) Observe the stability of system output under different load conditions and observe the working status of the photovoltaic array and battery pack at the same time

[0063] In this scenario, the peak voltage reference value of the system output is set to 400 V. At simulation time t = 0.4 s, the load resistance changes from 10 Ω to 7 Ω, and the load reactance remains unchanged.

[0064] The system output voltage is Figure 8 As shown in (a), the output voltage value does not change with the change of load and has strong stability. The voltage waveform is characterized by a 13-level step wave, which embodies the control strategy of the modular multi-level converter. As shown in the figure, at the peak moment of the AC output, the six modules work in the series mode for a longer time to reach a peak voltage of about 400V. At other times, the proportion of the connection mode of the six modules is different, which has flexible variable structure characteristics. In the whole cycle, the photovoltaic array always works near the maximum power point, and the average value of the maximum power tracking accuracy of the four photovoltaic arrays is above 99%, as shown in the figure. Fig. 9 The battery pack can be charged and discharged flexibly according to the load size, such as Fig.10 As shown in the figure, before t = 0.4s, when the load was light, the power generated by the four photovoltaic arrays not only met the load demand, but also supplied power to the two battery packs, and their SOC curves rose. After t = 0.4s, the load became heavier, causing the charging trend of the second battery pack to slow down, and the first battery pack even automatically switched to a discharge state.

[0065] The system output current value is as follows: Figure 8 As shown in (b), the output current value increases as the load becomes heavier, and the current waveform is also a 13-level step wave. When the reactance value in the load increases, the output current waveform becomes smoother and approximates a sine wave. This is the biggest advantage of using MMSPC. Compared with the traditional two-level converter, the system outputs less harmonic components, reducing the size and cost of the filter.

[0066] (2) Adjust the output reference value to observe the followability of the system output and observe the working status of the photovoltaic array and battery pack at the same time

[0067] In this scenario, the peak voltage reference value of the system output changes from 330 V to 400 V at simulation time t = 0.4 s, and the load remains unchanged.

[0068] The system output voltage is Fig.11 As shown in (a), the output voltage value changes with the change of the reference value, and has a strong followability. Moreover, when the reference value is 330V, only five sub-modules need to be connected in series near the peak moment of the system output, and the voltage waveform is an 11-level step wave. When the reference value returns to 400V, the voltage waveform returns to 13 levels, which once again confirms the flexible and reconfigurable characteristics of the converter.

[0069] System output current Fig.11 As shown in (b), the output current value also changes with the reference value, which is in line with expectations.

[0070] It can be seen from the above simulation results that the photovoltaic power generation-battery energy storage converter with reconfigurable function proposed in the present invention can make the submodules work flexibly in series, parallel, boost or bypass mode, avoiding the "short board effect" caused by aging, partial shadow or defects of traditional long photovoltaic string connection. The design of cascaded double H bridge concentrates all energy conversion links in one converter, reducing the loss during energy conversion. Compared with the traditional two-level converter, the multi-level control strategy reduces the harmonic components of the system output and improves the power quality. More importantly, the converter only needs to install coupling inductors between modules without the need for traditional boost circuits to achieve the maximum power tracking of each photovoltaic array, thereby improving the overall power generation of the system. The design of PV-BT-PV working cluster improves the system from being affected by "intermittent", and the battery pack can also be flexibly charged and discharged according to the weight of the load.

[0071] It should be noted that, in this specification, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the statement "includes a" does not exclude the presence of other identical elements in the process, method, article or device including the element.

[0072] The above embodiments are only used to help understand the method and core idea of ​​the present invention, but not to limit it. It should be noted that, for those skilled in the art, without departing from the principle of the present invention, several improvements or modifications can be made to the present invention, and these improvements and modifications also fall within the scope of protection of the present invention.

Claims

1. A photovoltaic power generation-battery energy storage converter with reconfigurable function, wherein the converter is connected to a photovoltaic array, a battery pack and a load respectively, characterized in that: The converter comprises: A first switch tube, a second switch tube, a third switch tube, a fourth switch tube, a fifth switch tube, a sixth switch tube, a seventh switch tube, an eighth switch tube and a coupled inductor, which form a cascaded double H-bridge structure; The drain of the first switch tube is connected to the source of the third switch tube to form a first bridge arm; The drain of the second switch tube is connected to the source of the fourth switch tube to form a second bridge arm; The drain of the fifth switch tube is connected to the source of the seventh switch tube to form a third bridge arm; The drain of the sixth switch tube is connected to the source of the eighth switch tube to form a fourth bridge arm; The source electrode of the first switch tube is short-circuited with the source electrode of the second switch tube and connected to the positive electrode of the photovoltaic array; The drain of the third switch tube is short-circuited with the drain of the fourth switch tube and connected to the negative electrode of the photovoltaic array; The source electrode of the fifth switch tube is short-circuited with the source electrode of the sixth switch tube and connected to the positive electrode of the battery pack; The drain of the seventh switch tube is short-circuited with the drain of the eighth switch tube and connected to the negative electrode of the battery pack; Two terminals of a coil of the coupled inductor are connected to the midpoints of the first bridge arm and the second bridge arm respectively; Two terminals of the other coil of the coupled inductor are connected to the midpoints of the third bridge arm and the fourth bridge arm respectively.

2. The photovoltaic power generation-battery energy storage converter with reconfigurable function as claimed in claim 1, characterized in that: The invention also includes a control circuit, wherein the control circuit includes a first control branch, a second control branch, and a modulation unit, and the first control branch and the second control branch are connected to the modulation unit; The first control branch is used to obtain the terminal voltage of the load and generate a first control signal to achieve constant voltage control at both ends of the load; The second control branch is used to obtain the output voltage of the photovoltaic array and the output current of the photovoltaic array, and generate a second control signal to achieve maximum power point tracking control of the photovoltaic array.

3. The converter with reconfigurable function as claimed in claim 2, characterized in that: The first control branch includes an adder and a PI controller, the second control branch includes MPPT control and inter-module current calculation, and the modulation unit includes modulation reference calculation of the converter, comparison of the modulation reference signal with a triangular carrier signal, and SPWM triggering of a cascaded double H-bridge converter.

4. A control method for a photovoltaic power generation-battery energy storage converter with a reconfigurable function, characterized in that: Applied to the reconfigurable converter according to any one of claims 1 to 3, the method specifically comprises: Acquiring a terminal voltage of the load and generating a first control signal; Acquire the output voltage and the output current of the photovoltaic array to generate a second control signal; The driving signals of the first to eighth switching tubes are generated according to the first control signal and the second control signal.

Images