Bipolar output high-voltage synchronous BUCK circuit and control method thereof

Abstract

The invention discloses a bipolar output high-voltage synchronous BUCK circuit and a control method thereof, and relates to the technical field of circuits. The drain electrode of a switch tube Q1 is connected with the positive electrode of a voltage input end, and the source electrode of the switch tube Q1 is connected with the drain electrode of a switch tube Q3; the source electrode of the Q3 is connected with one end of an inductor L, and the other end of the inductor L is connected with a voltage output end; the drain electrode of the Q2 is connected between the source electrode of the Q1 and the drain electrode of the Q3, and the source electrode of the Q2 is connected with the negative electrode of the voltage input end; the source electrode of the Q4 is connected with the source electrode of the Q2, and the drain electrode is connected to the voltage output end; the drain electrode of the Q5 is connected between the drain electrode of the Q2 and the drain electrode of the Q3, and the source electrode of the Q5 is connected between the drain electrode of the Q4 and the voltage output end; the source electrode of the Q6 is connected between the source electrode of the Q4 and the source electrode of the Q2, and the drain electrode of the Q6 is connected between the source electrode of the Q3 and the inductor L; the circuit meets special application scenes of high power density, high voltage and bipolar output.

Description

Technical Field

[0001] The present invention relates to the technical field of circuit control, and in particular to a high-voltage synchronous BUCK circuit with bipolar output and a control method thereof. Background Art

[0002] With the widespread application of piezoelectric ceramics in the field of micro-drive, scholars at home and abroad have conducted in-depth research on piezoelectric ceramic drive power supplies and developed various piezoelectric drive power supplies. Among them, high-voltage drive power supplies are widely used due to their simple structure and stable performance. Low-voltage drive power supplies have the characteristics of small size, light weight and high reliability. Voltage-type piezoelectric drive power supplies and current / charge-type piezoelectric drive power supplies are the two most widely used drive power supplies at present, but there are still problems such as low power density, low conversion efficiency and low drive voltage that need to be solved.

[0003] At present, some scholars have proposed: (1) A high-dynamic driving power supply for inertial stick-slip, which significantly improves the switching speed of the power MOSFET by optimizing the charging and discharging loop parameters of the power MOSFET, thereby improving the response performance of the driving power supply. When driving a 0.5uF inertial stick-slip load, the step response time of the driving power supply is 40us; in terms of stability, the phase margin of the power amplifier circuit is 80°, and the circuit has good static characteristics and dynamic response performance; (2) A simulation model of a piezoelectric bending driver and its amplifier circuit is proposed for the piezoelectric bending driver, and the influence of the current limitation of the amplifier circuit on the performance of the piezoelectric bending driver is tested. An audio amplifier is developed. The circuit can provide a high-voltage output of 200V under a capacitive load of 1uF; when driving a 0.1uF load, its transition frequency can reach 10KHz; (3) Based on the principle of error amplification, a method of amplifying the output voltage of the dynamic power amplifier by using a high-voltage operational amplifier connected in series with the power amplifier part is proposed and analyzed using class AB A method for connecting multiple power boost units in parallel in a complementary symmetrical power amplifier circuit to increase the output current and output power peak. Using the proposed principle and method, a high-voltage high-power amplifier for driving a piezoelectric stack actuator was developed, and it was simulated and tested. When driving a 4.7uF capacitive load, the power amplifier circuit can output a 150V, 100Hz frequency sine square wave triangle wave signal without distortion, and the step-up and step-down times are both less than 500us; (4) A 15W power amplifier, the power amplifier circuit is mainly composed of a flyback converter and a power operational amplifier. The flyback converter generates a variable DC voltage to power the P-OPA, and the P-OPA outputs an amplified sinusoidal signal with a DC bias of 100V to drive the piezoelectric actuator. The power amplifier circuit can output a 0-10kHz, 200V sinusoidal signal without distortion when it is unloaded. When driving a 1uF load, the output sinusoidal signal frequency can reach 200Hz; the step-up time of the no-load output 200V high voltage is less than 15us.

[0004] At present, when the piezoelectric driver drives a 0.5uF load, the step response time is much longer than 40us; as the application demand for fast driving of piezoelectric ceramics becomes higher and higher, the performance of the driver also needs to match it. However, the current general capacitive high-voltage driver cannot meet the requirements of a certain load power when solving the bipolar output problem. The power density of the driver made of high-power devices is relatively low, resulting in the inability of the capacitive load driver to meet the special application scenarios of high power density, high voltage and bipolar output. Summary of the invention

[0005] In view of the fact that the power density of the driving power supply made of high-power devices in the prior art is relatively low, resulting in the inability of the capacitive load driving power supply to meet special application scenarios of high power density, high voltage and bipolar output, the present invention proposes a high-voltage synchronous BUCK circuit with bipolar output and a control method thereof, thereby solving the problems existing in the prior art.

[0006] A bipolar output high-voltage synchronous BUCK circuit includes main switch tubes Q1 and Q2, commutation switch tubes Q3, Q4, Q5 and Q6, and a front-stage voltage stabilizing capacitor C1, a filter capacitor C2, a filter inductor L and a resistor Rload;

[0007] The drain of Q1 is connected to the positive electrode of the voltage input terminal, and the source is connected to the drain of Q3; the source of Q3 is connected to one end of the inductor L, and the other end of the inductor L is connected to the voltage output terminal; the drain of Q2 is connected between the source of Q1 and the drain of Q3, and the source of Q2 is connected to the negative electrode of the voltage input terminal; the source of Q4 is connected to the source of Q2, and the drain is connected to the voltage output terminal; the drain of Q5 is connected between the drain of Q2 and the drain of Q3, and the source is connected between the drain of Q4 and the voltage output terminal; the source of Q6 is connected between the source of Q4 and the source of Q2, and the drain is connected between the source of Q3 and the inductor L; one end of Rload is connected to one end of the inductor connected to the voltage output terminal, and the other end is respectively connected to the source of Q5 and the drain of Q4; C2 is connected in parallel to both ends of Rload.

[0008] Furthermore, the operating modes of the bipolar output high voltage synchronous BUCK circuit include:

[0009] When Q1 is turned on, Q2 is turned off, Q3 and Q4 are turned on, Q5 and Q6 are turned off, and the current flows through Q1 and Q3, and then through the inductor L, Rload, and Q4 back to the negative pole of the power supply. At the same time, the inductor L and the capacitor C2 begin to charge;

[0010] When Q1 is turned off, Q2 is turned on, Q3 and Q4 are turned on, and Q5 and Q6 are turned off. At this time, the inductor L and the capacitor C2 begin to discharge and continue to supply power to the output end;

[0011] When Q1 is turned on, Q2 is turned off, Q5 and Q6 are turned on, Q3 and Q4 are turned off, and the current flows through the switch tubes Q1, Q5, and Rload, and then through the inductor L and the switch tube Q6 back to the negative pole of the power supply. At the same time, the inductor L and the capacitor C2 begin to charge;

[0012] When Q1 is turned off, Q2 is turned on, Q5 and Q6 are turned on, and Q3 and Q4 are turned off. At this time, the inductor L and the capacitor C2 begin to discharge and continue to supply power to the output end.

[0013] Furthermore, a capacitor C1 is connected in parallel between two ends of the voltage input terminal.

[0014] Furthermore, the capacitor C2 is connected in series with a resistor R.

[0015] The present invention also includes a control method for a high-voltage synchronous BUCK circuit with bipolar output, comprising the following steps:

[0016] The high-voltage signal is input into the high-voltage synchronous BUCK circuit with bipolar output to generate a pulse wave with adjustable duty cycle; at the same time, three PWM waves are generated through FPGA, one of which is used to control the main switch tubes Q1 and Q2 to complete synchronous rectification, and the other two PWM waves are used to control the current direction by controlling the commutation switch tubes Q3, Q4, Q5 and Q6;

[0017] The pulse wave with adjustable duty cycle is filtered by an LC filter to obtain low-voltage direct current; the output voltage amplitude is controlled by adjusting the duty cycle of the PWM wave, and the output voltage polarity is controlled by switching the switch tubes Q3, Q4, Q5 and Q6. When Q3 and Q4 are turned on and Q5 and Q6 are turned off, a positive polarity voltage is output, and when Q3 and Q4 are turned off and Q5 and Q6 are turned on, a negative polarity voltage is output.

[0018] The present invention provides a bipolar output high voltage synchronous BUCK circuit and a control method thereof, which have the following beneficial effects:

[0019] The present invention proposes a high-voltage synchronous BUCK circuit topology with bipolar output, which completes synchronous rectification by controlling the main switch tubes Q1 and Q2, and controls the output voltage polarity by reversing switch tubes Q3, Q4, Q5, and Q6 to obtain a continuously adjustable and direction-controllable DC voltage, and provide a stable, continuously adjustable bidirectional DC voltage. The circuit meets special application scenarios of high power density, high voltage, and bipolar output. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Three basic topological structures of the DC-DC converter in the embodiments of the present invention, (a) is a Buck type DC-DC topological structure, (b) is a Buck type DC-DC topological structure, and (c) is a Buck-Boost type DC-DC topological structure;

[0021] Figure 2 Schematic diagram of a synchronous rectification type Buck circuit in an embodiment of the present invention;

[0022] Figure 3 A schematic diagram of a bidirectional Buck topology structure in an embodiment of the present invention;

[0023] Figure 4Schematic diagram of the topological structure of the high-voltage synchronous BUCK circuit with bipolar output in working state 1 according to an embodiment of the present invention;

[0024] Figure 5 Schematic diagram of the topological structure of the high-voltage synchronous BUCK circuit with bipolar output in working state 2 in an embodiment of the present invention;

[0025] Figure 6 Schematic diagram of the topological structure of the high-voltage synchronous BUCK circuit with bipolar output in working state 3 in an embodiment of the present invention;

[0026] Figure 7 Schematic diagram of the topological structure of the high-voltage synchronous BUCK circuit with bipolar output in working state 4 in an embodiment of the present invention;

[0027] Figure 8 It is a block diagram of the overall structure of the hardware circuit in an embodiment of the present invention;

[0028] Fig. 9 This is a flow chart of voltage loop design in an embodiment of the present invention;

[0029] Fig.10 This is a flow chart of current loop design in an embodiment of the present invention;

[0030] Fig.11 This is a PID structure diagram in an embodiment of the present invention;

[0031] Fig.12 This is a Buck circuit simulation diagram in an embodiment of the present invention;

[0032] Fig.13 Schematic diagram of a modulation signal wave in an embodiment of the present invention;

[0033] Fig.14 Schematic diagram of output load voltage simulation in an embodiment of the present invention. DETAILED DESCRIPTION

[0034] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0035] The present invention proposes a bipolar output high-voltage synchronous BUCK circuit, which controls the opening and closing of the gallium nitride switch tube by outputting PWM waves through FPGA, so that the power circuit outputs the corresponding voltage to the piezoelectric ceramic, and uses the piezoelectric fiber composite material (Macro Fiber Composite, MFC) as an actuator and sensor according to the forward and reverse piezoelectric effect. The converter adopts current mode control to improve the transient response speed. In order to avoid the subharmonic oscillation problem caused by the peak current mode when the circuit duty cycle is greater than 50%, the circuit adopts a fixed slope slope compensation technology to avoid circuit oscillation while ensuring that the load capacity meets the requirements. The converter designed by the present invention is equipped with a variety of protection circuits, including: soft start circuit, dead time control circuit, absorption circuit, etc., which improves the reliability of the converter. The new bipolar output high-voltage synchronous BUCK circuit designed by the present invention has the advantages of simple structure, excellent performance, low failure rate, etc. The converter is suitable for portable electronic devices, aerospace, medical equipment and other scenes, has high power density and small size, and provides stable, continuously adjustable bidirectional DC voltage to each module in the system. In order to solve the problem of stable output of fixed voltage, a PID control algorithm was used to establish the parameters fed back to the FPGA, achieving the goal of high-precision control of the piezoelectric fiber composite MFC.

[0036] The three basic topological structures of DC-DC converters are analyzed; the function of DC-DC converters is to convert the input DC voltage into the output DC voltage, which can achieve step-up or step-down conversion. DC-DC converters are switching power supplies, which modulate the input DC voltage into a controllable square wave through a control circuit in a switching manner, and achieve energy conversion with different connection methods of the energy storage device inductor and capacitor. According to the different connection methods of the inductor in the topological structure, three different functions of step-down, step-up, and step-down can be achieved. When the inductor is connected to the output load of the circuit, a Buck converter is formed, which can achieve step-down conversion of the output voltage to the input voltage; when the inductor is connected to the input power supply of the circuit, a Boost converter is formed, which can achieve step-up conversion of the output voltage to the input voltage; when the inductor is connected to the reference ground of the circuit (i.e., the negative pole of the power supply), a Buck-Boost converter is formed, which can achieve step-up and step-down conversion of the output voltage to the input voltage.

[0037] Figure 1 These are the three basic topologies of DC-DC converters. To analyze the topology of the converter, we can start from the characteristics of the inductor. Since the current on the inductor does not change suddenly, the rate of change of the inductor current follows the equation described by equation (1):

[0038]

[0039] Where V represents the voltage difference across the inductor, L is the value of the inductor, and ΔI / Δt is the rate of change of the inductor current. The switching process of the DC-DC converter corresponds to the charging and freewheeling process of the inductor. In one clock cycle T, the charging time of the converter is Δt. on , the continuous current time is Δt off , and T = Δt on +Δt off The inductance equation in the charging phase and the inductance equation in the freewheeling phase are obtained by equation (1):

[0040]

[0041] Among them, V ON and V OFF Respectively represent the voltage across the inductor during the charging and freewheeling stages, ΔI ON and ΔI OFF Represent the change of inductor current in charging and freewheeling phases respectively. Assuming that the start and end values ​​of inductor current in a cycle do not change, combined with equations (2) and (3), the volt-second balance theorem is obtained. The product of the voltage on the inductor and the duration is volt-second. The duty cycle D represents the proportion of conduction time in a cycle.

[0042]

[0043] Analysis of Buck topology, Boost topology and Buck-Boost topology:

[0044] exist Figure 1 In the Buck topology shown in (a), the forward voltage drop of the freewheeling diode is ignored, V ON =V in -V out , V OFF =V out According to the volt-second balance theorem of formula (4), we can obtain:

[0045] (V in -V out )·D·T=V out ·(1-D)·T (6)

[0046] After simplification, the relationship between input and output voltage and duty cycle D is obtained:

[0047] V out =D·V in (7)

[0048] exist Figure 1 In the Boost topology shown in (b), V ON =V in , V OFF=V out -V in According to the volt-second balance theorem, we get:

[0049] V in ·D·T=(V out -V in )·(1-D)·T(8)

[0050] After simplification, the relationship between input and output voltage and duty cycle D is obtained:

[0051]

[0052] exist Figure 1 In the Buck-Boost topology shown in (c), unlike the Buck and Boost types, the output voltage in the Buck-Boost topology has the opposite polarity to the input voltage, V ON =V in , V OFF =-V out According to the volt-second balance theorem, we get:

[0053] V in ·D·T=-V out ·(1-D)·T (10)

[0054] After simplification, the relationship between input and output voltage and duty cycle D is obtained:

[0055]

[0056] Since the duty cycle D varies between 0 and 1, the voltage conversion function can be seen from the input and output relationship of the above topological structures. Table 1 summarizes the above topological structures.

[0057] Table 1 Basic topology of converter

[0058]

[0059] Synchronous rectification: Buck power supply is a step-down switching power supply that can convert high-voltage DC into low-voltage DC. Buck power supplies are widely used in automobiles, industry, telecommunications, networks, and consumer electronics. Traditional Buck power supplies use Schottky diodes for freewheeling. This working mode improves the output-to-input ratio compared to linear voltage regulators, but Schottky diodes produce large conduction losses, greatly reducing power efficiency. In order to improve power efficiency, Buck power supplies are designed using synchronous rectification, using synchronous rectification MOS tubes instead of Schottky diodes. The on-resistance of MOS tubes is generally only in the milliohm range, and when outputting large currents, the loss is much lower than that of Schottky diodes.

[0060] The present invention uses FPGA to generate PWM wave with adjustable duty cycle and synchronous rectification circuit structure, and collects the voltage fed back by the main control FPGA in real time for PID closed-loop control, so that the output voltage reaches the set threshold, which improves the overall performance of the Buck power supply to a certain extent. The basic structure of the synchronous rectification Buck power supply is as follows Figure 2 As shown, a MOS tube is used instead of a freewheeling diode. In this circuit, when Q is turned on, D is turned off; when Q is turned off, D is turned on, thus avoiding the dead zone voltage caused by the freewheeling diode, greatly improving the power supply efficiency and reducing the ripple.

[0061] The present invention proposes a novel bidirectional synchronous DC-DC BUCK circuit, such as Figure 3 As shown in the figure, the hardware of the Buck power supply circuit is mainly composed of switch tubes such as Q1, Q2, Q3, Q4, Q5, Q6, and the front-stage voltage stabilizing capacitor C1, resistor R, resistor Rload, capacitor C2 and inductor L. Each switch tube is controlled by the PWM wave output by the FPGA, as shown in Figure 3 As shown. The drain of Q1 is connected to the positive electrode of the voltage input terminal, and the source is connected to the drain of Q3; the source of Q3 is connected to one end of the inductor L, and the other end of the inductor L is connected to the voltage output terminal; the drain of Q2 is connected between the source of Q1 and the drain of Q3, and the source of Q2 is connected to the negative electrode of the voltage input terminal; the source of Q4 is connected to the source of Q2, and the drain is connected to the voltage output terminal; the drain of Q5 is connected between the drain of Q2 and the drain of Q3, and the source is connected between the drain of Q4 and the voltage output terminal; the source of Q6 is connected between the source of Q4 and the source of Q2, and the drain is connected between the source of Q3 and the inductor L; one end of Rload is connected to one end of the inductor connected to the voltage output terminal, and the other end is respectively connected to the source of Q5 and the drain of Q4; C2 is connected in parallel to both ends of Rload.

[0062] Circuit switch status analysis:

[0063] like Figure 4 As shown, when the main switch tube Q1 is turned on, the freewheeling switch tube Q2 is turned off, the switch tubes Q3 and Q4 are turned on, and the switch tubes Q5 and Q6 are turned off. The current flows through the switch tubes Q1 and Q3, and then to the inductor L and Rload. The switch tube Q4 returns to the negative pole of the power supply, and the inductor L and the capacitor C2 begin to charge.

[0064] like Figure 5 As shown, when the main switch tube Q1 is turned off, the freewheeling switch tube Q2 is turned on, the switch tubes Q3 and Q4 are turned on, and the switch tubes Q5 and Q6 are turned off. At this time, the inductor L and the capacitor C2 begin to discharge and freewheel to supply power to the output load.

[0065] like Figure 6As shown, when the main switch tube Q1 is turned on, the freewheeling switch tube Q2 is turned off, the switch tubes Q5 and Q6 are turned on, and the switch tubes Q3 and Q4 are turned off. The current flows through the switch tubes Q1, Q5, Rload, and then to the inductor L. The switch tube Q6 returns to the negative pole of the power supply, and the inductor L and the capacitor C2 begin to charge.

[0066] like Figure 7 As shown, when the main switch tube Q1 is turned off, the freewheeling switch tube Q2 is turned on, the switch tubes Q5 and Q6 are turned on, and the switch tubes Q3 and Q4 are turned off. At this time, the inductor L and the capacitor C2 begin to discharge and freewheel to supply power to the output load.

[0067] Based on the above-mentioned bipolar output high-voltage synchronous BUCK circuit topology structure, the present invention also proposes a control method for a bipolar output high-voltage synchronous BUCK circuit, comprising the following steps:

[0068] The high-voltage signal is input into the high-voltage synchronous BUCK circuit with bipolar output to generate a pulse wave with adjustable duty cycle; at the same time, three PWM waves are generated through FPGA, one of which is used to control the main switch tubes Q1 and Q2 to complete synchronous rectification, and the other two PWM waves are used to control the current direction by controlling the commutation switch tubes Q3, Q4, Q5 and Q6.

[0069] The pulse wave with adjustable duty cycle is filtered by an LC filter to obtain low-voltage direct current; the output voltage amplitude is controlled by adjusting the duty cycle of the PWM wave, and the output voltage polarity is controlled by reversing the switch tubes Q4, Q5 and Q6. When Q3 and Q4 are turned on and Q5 and Q6 are turned off, a positive polarity voltage is output, and when Q3 and Q4 are turned off and Q5 and Q6 are turned on, a negative polarity voltage is output.

[0070] The hardware of synchronous bidirectional Buck power supply circuit is mainly composed of FPGA main control unit, auxiliary power supply circuit, bidirectional Buck circuit, voltage and current sampling circuit and drive circuit. Figure 8As shown. This circuit generates an independent PWM wave through FPGA to control the main control MOS tube to complete the synchronous rectification process, and the other two PWM waves control the remaining switch tubes to achieve the purpose of controlling the current direction. Since the PWM wave generated by FPGA has small voltage and current and weak load capacity, it cannot start and shut down the MOS tube. Therefore, the PWM wave generated by FPGA must be generated by a dedicated drive circuit to generate a PWM wave with strong load capacity, thereby controlling the high-voltage MOS tubes Q1 and Q2. In the main power topology, the high-voltage signal is chopped by the BUCK circuit to generate a pulse wave with adjustable duty cycle, which is then filtered by the LC filter to obtain low-voltage DC power. The output voltage amplitude is controlled by adjusting the duty cycle of the PWM wave to obtain a continuously adjustable DC voltage. The branch switch tubes of Q3-Q6 control the output voltage polarity. When Q3 and Q4 are turned on and Q5 and Q6 are turned off, a positive polarity voltage is output; when Q3 and Q4 are turned off and Q5 and Q6 are turned on, a negative polarity voltage is output; thus, a continuously adjustable and direction-controllable DC voltage is obtained.

[0071] PID control technology: PID algorithm contains the main information of the past, present and future in the dynamic control process. Among them, the proportion (P) represents the current information, plays the role of correcting the deviation, and makes the process respond quickly. The integral (I) represents the information accumulated in the past, which can eliminate the static error and improve the static characteristics of the system. The differential (D) has a leading control effect when the signal changes, and represents the future information. At the beginning of the process, the process is forced to accelerate, and at the end of the process, the overshoot is reduced, the oscillation is overcome, the stability of the system is improved, and the transition process of the system is accelerated. The three functions are properly coordinated to make the dynamic process fast, stable, accurate, and achieve good results. The control algorithm does not rely too much on the system parameters during the design process, so the change of the system parameters has little effect on the control effect, and the control has good adaptability and strong robustness. Therefore, PID control is widely used in engineering practice for its simplicity and easy parameter setting. However, most of the early linear power supplies were analog PID control, which simply adopted the instantaneous value feedback of the output voltage. Its performance, especially the dynamic performance and when the load is nonlinear, the control effect is not satisfactory. A lot of research has been done to this end, and the instantaneous values ​​of the output inductor current and the output filter capacitor current have been introduced into the control system, which has greatly improved the output characteristics of the linear power supply. However, the huge analog control circuit reduces the reliability of the control system, makes debugging complicated, and is not easy to adjust. With the emergence of FPGA, this problem has been quickly solved. Nowadays, various compensation measures have been conveniently applied to the digital PID control of linear power supplies. The introduction of voltage and current control has improved the digital PID control effect of linear power supplies.

[0072] Digital PI regulator: After years of development, PID has continuously improved its performance, accumulated more and more experience, and has been widely used in industrial control. The application of microcomputers and microprocessors in PID control has further developed PID control, and nonlinear PID control algorithms, selective PID control algorithms, and adaptive PID control algorithms have emerged. All of these algorithms are developed on the basis of the basic PID algorithm.

[0073] Basic PI algorithm: The output of the regulator is the sum of two components, which are proportional to the input (error) of the regulator and proportional to the integral of the input. Its continuous expression is:

[0074]

[0075] Where: e is the error between the feedback value and the given value, T I is the integration time, K p is the gain factor of the regulator, and u is the output signal of the regulator.

[0076] By performing pull-type transformation on both sides of the above equation, the transfer function of the PI regulator can be obtained:

[0077]

[0078] where U(s) and E(s) are the Latent transformations of u and e respectively.

[0079] The proportional term in PI control is used to correct the deviation, and the integral term is used to eliminate the steady-state error of the system. The performance of the PI regulator depends on K p , T I The task of designing and adjusting the digital PI regulator is to select the appropriate PI model according to the controlled object and system requirements, and to discretize the model using appropriate methods, so that it can be realized by computer, and finally determine K p , T I and sampling period T0.

[0080] By using different methods to discretize D(s), we can get many different digital PI regulator algorithms. The following briefly introduces the basic digital PI position algorithm and the more commonly used digital PI control incremental algorithm.

[0081] Positional PI algorithm: Replace the integral term with the rectangular method numerical integration, and we get:

[0082]

[0083] in u0 is the initial output of the regulator. If the initial control condition is zero, then u0 = 0; e kt k The error value at the moment; u k t k The output of the regulator at that moment;

[0084] Using the trapezoidal method to numerically integrate the integral term, we can obtain:

[0085]

[0086] The trapezoidal method is more accurate than the rectangular method, but when the sampling period is small enough, the difference between the two is not significant.

[0087] Incremental PI algorithm: From formula (15), we can get:

[0088]

[0089] From equations (15) and (16), the increment of the regulator output can be obtained as:

[0090]

[0091] The incremental calculation error has little effect on the control quantity. The incremental algorithm only needs to calculate, store and output Δu. The number of bits of computers and microprocessors is limited, so higher accuracy can be obtained. The impact on the system is small when switching between automatic and manual. Whether it is computer automatic control or manual control, the control quantity Δu of the incremental algorithm is very small, and the previous control quantity u k-1 It has been stored in the integral device, so the switching will not cause a big impact on the system. Incremental calculation has high reliability. Even if the computer or microprocessor fails and Δu=0, the system can still be switched at u k-1 It maintains the original working state under the action of, thus improving the reliability of the system.

[0092] Anti-integral saturation: When the system is disturbed or the given input changes in step, the system will have a large deviation. After the integral term is accumulated, the control amount may exceed the limit determined by the mechanical or physical performance. This phenomenon is called "saturation". The saturation of the control amount is mainly caused by the saturation of the integral term. Integral saturation will cause a large overshoot and long-term fluctuation of the controlled amount, which is not good for the control system. One way to solve this problem is to limit the control amount of the PI output. Assume that the upper limit value of the voltage of the bidirectional Buck output is u max , the lower limit is u min , you can perform the following operations:

[0093] When u(k)>u max When u(k)=u max , cancel the integral operation; when u(k)<u max When u(k)=u max, cancel the integral operation; when u min ≤u(k)≤u max When , the integral operation is performed and the calculated value u(k) is output.

[0094] Digital PI parameter setting: The task of digital PID regulator parameter setting is to determine k p , T I And parameters such as sampling period T0.

[0095] For simple systems, these parameters can be determined by theoretical calculation, but for slightly more complex systems, theoretical calculation is more difficult. Engineering methods are generally used to adjust parameters, such as empirical method, attenuation curve method, critical proportion method and response curve method. Regardless of the PI parameter adjustment method used, the parameters should be further verified and corrected in the closed loop of the system in order to achieve better system performance. During the correction process, attention should always be paid to the impact of various PI parameters on system performance: (1) Increase the proportional coefficient k p , which will speed up the system response and reduce the static error, but the overshoot will increase and the stability will deteriorate; (2) Increase the integral time T I , the integral effect is weakened, the overshoot is reduced, the system stability is better, but the time to eliminate the system static error is prolonged.

[0096] System software structure: The system software mainly consists of two parts: the main program and the interrupt service subroutine. Because this system has high requirements for the real-time processing capability of the software, most of the functional modules are completed in the interrupt subroutine. In the main program, the program first sets some registers and initializes all variables. Then enable the required interrupts, start the timer, and wait in a loop. The interrupt service subroutine is the periodic interrupt program of timer 2. In the interrupt subroutine, FPGA mainly completes the sampling of output voltage and inductor current, the control algorithm of voltage loop and current loop, the output of PWM wave, and starts the next A / D conversion.

[0097] Generation of reference sine wave: The reference sine wave is made into a table. After setting the timer, in each switching cycle (interrupt cycle of the timer), the FPGA program obtains the corresponding digital quantity from the reference sine wave table according to the table pointer. At the same time, the table pointer is increased by one, and the table pointer is reset to the first address of the reference sine wave table at the end of a sine wave cycle.

[0098] Design of voltage loop: DSP instruction cycle is 33ns, and most instructions are single-cycle instructions, and AD conversion time is 375ns. These characteristics enable DSP to fully control the output voltage of the inverter point by point, so the voltage outer loop uses the instantaneous value feedback of the output voltage and compares it with the reference sinusoidal voltage to stabilize the output voltage at the set value and suppress the distortion of the output voltage. The voltage regulator samples the proportional integral (PI) regulation. The program flow chart is as follows Fig. 9 shown.

[0099] Design of current loop: The feedback signal of the current loop is the inductor current, which is proportionally regulated. The inductor current is equal to the load current plus the filter capacitor current, and the filter capacitor current is the differential of the output voltage. Therefore, the current loop feedback is equivalent to adding a proportional differential lead correction network to the voltage feedback, which can make the system more stable. At the same time, the inductor current includes the load current, so it plays a role in limiting the current. The program flow chart is as follows Fig.10 shown.

[0100] PWM PID closed-loop circuit design: the fundamental frequency is F s With the carrier amplitude F c The ratio is called the carrier ratio and is represented by P:

[0101]

[0102] However, in practical applications, due to switching losses, unstable power supply pressure and other reasons, the actual output voltage will deviate from the theoretical value. This system uses PID control to quickly eliminate the deviation and make the output reach the expected voltage. Because changing the modulation size can change the amplitude of the output voltage, the modulation signal is used as the control object of the PID controller. The closed-loop control structure diagram is shown in the figure. Fig.11 shown.

[0103] MATLAB / Simulink simulation: Build a power circuit on MATLAB. Its overall structure is as follows Fig.12 Here, a triangular carrier and a modulation signal are used to generate a PWM wave, as shown in Fig.13 After the construction is completed, the simulation is started and the voltage waveform of the capacitive load is measured, as shown in Fig.14 shown.

[0104] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A bipolar output high voltage synchronous BUCK circuit, characterized in that: It includes main switch tubes Q1 and Q2, commutation switch tubes Q3, Q4, Q5 and Q6, and a front-stage voltage stabilizing capacitor C1, a filter capacitor C2, a filter inductor L and a resistor Rload; The drain of Q1 is connected to the positive electrode of the voltage input terminal, and the source is connected to the drain of Q3; the source of Q3 is connected to one end of the inductor L, and the other end of the inductor L is connected to the voltage output terminal; the drain of Q2 is connected between the source of Q1 and the drain of Q3, and the source of Q2 is connected to the negative electrode of the voltage input terminal; the source of Q4 is connected to the source of Q2, and the drain is connected to the voltage output terminal; the drain of Q5 is connected between the drain of Q2 and the drain of Q3, and the source is connected between the drain of Q4 and the voltage output terminal; the source of Q6 is connected between the source of Q4 and the source of Q2, and the drain is connected between the source of Q3 and the inductor L; one end of Rload is connected to one end of the inductor connected to the voltage output terminal, and the other end is respectively connected to the source of Q5 and the drain of Q4; C2 is connected in parallel to both ends of Rload.

2. A bipolar output high voltage synchronous BUCK circuit according to claim 1, characterized in that: The operating modes of the bipolar output high voltage synchronous BUCK circuit include: When Q1 is turned on, Q2 is turned off, Q3 and Q4 are turned on, Q5 and Q6 are turned off, and the current flows through Q1 and Q3, and then through the inductor L, Rload, and Q4 back to the negative pole of the power supply. At the same time, the inductor L and the capacitor C2 begin to charge; When Q1 is turned off, Q2 is turned on, Q3 and Q4 are turned on, and Q5 and Q6 are turned off. At this time, the inductor L and the capacitor C2 begin to discharge and continue to supply power to the output end; When Q1 is turned on, Q2 is turned off, Q5 and Q6 are turned on, Q3 and Q4 are turned off, and the current flows through the switch tubes Q1, Q5, and Rload, and then through the inductor L and the switch tube Q6 back to the negative pole of the power supply. At the same time, the inductor L and the capacitor C2 begin to charge; When Q1 is turned off, Q2 is turned on, Q5 and Q6 are turned on, and Q3 and Q4 are turned off. At this time, the inductor L and the capacitor C2 begin to discharge and continue to supply power to the output end.

3. The high-voltage synchronous BUCK circuit with bipolar output according to claim 1, characterized in that: The two ends of the voltage input terminal are connected in parallel with a capacitor C1.

4. The high-voltage synchronous BUCK circuit with bipolar output according to claim 1, characterized in that: The capacitor C2 is connected in series with a resistor R.

5. A control method for a high voltage synchronous BUCK circuit with bipolar output according to claim 1, characterized in that: The following steps are involved: The high-voltage signal is input into the high-voltage synchronous BUCK circuit with bipolar output to generate a pulse wave with adjustable duty cycle; at the same time, three PWM waves are generated through FPGA, one of which is used to control the main switch tubes Q1 and Q2 to complete synchronous rectification, and the other two PWM waves are used to control the current direction by controlling the commutation switch tubes Q3, Q4, Q5 and Q6; The pulse wave with adjustable duty cycle is filtered by an LC filter to obtain low-voltage direct current; the output voltage amplitude is controlled by adjusting the duty cycle of the PWM wave, and the output voltage polarity is controlled by switching the switch tubes Q3, Q4, Q5 and Q6. When Q3 and Q4 are turned on and Q5 and Q6 are turned off, a positive polarity voltage is output, and when Q3 and Q4 are turned off and Q5 and Q6 are turned on, a negative polarity voltage is output.

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