Four-switch buck-boost motor PAM modulation method and control method based on fuel cell

Abstract

A four-switch buck-boost motor PAM modulation method and control method based on a fuel cell can increase the voltage of the hydrogen fuel cell to meet the needs of driving the air compressor. At the same time, the DC bus voltage can be changed to meet the U at the commutation time of the brushless DC motor. dc =4E, ensuring that the output torque pulsation of the brushless DC motor is reduced when it is running at high speed and with load. At the same time, the commutation overlap method is adopted, and the hardware detection current zero-crossing technology is used to determine the relevant off-time of the delayed shutdown of the switching, which reduces the amount of calculation and is more accurate and simple. In addition, the PAM modulation method is adopted, the inverter conducts two phases and remains normally open, the commutation frequency is consistent with the speed, the number of switching tube actions is reduced, the switching loss is reduced, the efficiency of the drive system is improved, and the stability of the system is improved.

Description

Technical Field

[0001] The present invention relates to the field of hydrogen fuel cell air compressor control, in particular to a four-switch buck-boost motor PAM modulation method and a control method based on a fuel cell. Background Art

[0002] In recent years, with the rapid development of the hydrogen fuel cell industry, the research on the air compressor system of hydrogen fuel cells has received extensive attention from scientific researchers. The fuel cell voltage is low and cannot meet the needs of driving the air compressor. Therefore, it is necessary to add a pre-stage boost DC / DC topology structure. At the same time, the air compressor works in an ultra-high-speed operation state and uses a six-step commutation mode of a brushless DC motor (BLDCM), which puts forward greater requirements and challenges for the modulation method of the three-phase inverter. At the same time, the brushless DC motor drive system has the problem that the inductor current cannot change suddenly during commutation, and the electromagnetic torque pulsates. In severe cases, it can reach more than 50% of the output torque, which limits the use of the brushless DC motor drive control system in hydrogen fuel cell air compressor applications. In order to suppress the electromagnetic torque pulsation, adjust the DC bus voltage, and improve the system efficiency, a four-switch buck-boost motor PAM modulation method and control method based on fuel cells are proposed. Summary of the invention

[0003] The brushless DC motor drive control system has problems such as low efficiency and electromagnetic torque pulsation, which limit its application in the field of air compressors. The present invention provides a four-switch buck-boost motor PAM modulation method and control method based on a fuel cell, which increases the voltage of the hydrogen fuel cell to meet the needs of driving the air compressor, and can also change the DC bus voltage to meet the U dc =4E, ensuring that the output torque pulsation of the brushless DC motor is reduced when it is running at high speed and with load. At the same time, the commutation overlap method is adopted, and the hardware detection current zero-crossing technology is used to determine the relevant off-time of the delayed shutdown of the switching, which reduces the amount of calculation and is more accurate and simple. In addition, the PAM modulation method is adopted, the inverter conducts two phases and remains normally open, the commutation frequency is consistent with the speed, the number of switching tube actions is reduced, the switching loss is reduced, the efficiency of the drive system is improved, and the stability of the system is improved.

[0004] The present invention provides a four-switch buck-boost motor PAM modulation method based on a fuel cell, the specific steps are as follows, and the characteristics are as follows:

[0005] S1. According to the brushless motor parameters and the actual current and voltage received, a back electromotive force observer is constructed to obtain the back electromotive force of the brushless DC motor in real time.

[0006] S2, estimating the rotor position based on the received actual voltage and actual current information;

[0007] S3, calculating a current reference value according to the received actual speed and a preset speed reference value, and calculating a DC bus voltage reference value according to the received actual current and the current reference value;

[0008] S4, calculating the duty cycle D of the four-switch buck-boost according to the received actual power supply voltage and the DC bus voltage reference value;

[0009] S5. Determine the PAM modulation frequency according to the received actual rotation speed.

[0010] As a further improvement of the modulation method of the present invention, the step S1 is specifically as follows:

[0011] S1.1. Construct the motor terminal voltage equation based on the motor model;

[0012]

[0013] u x is the phase voltage, and the subscript x represents the three-phase winding a, b, and c;

[0014] i x is the phase current;

[0015] e x is the opposite electromotive force;

[0016] u N is the voltage between the neutral point of the motor and the ground;

[0017] R x is the phase resistance, R in the three-phase symmetrical winding a =R b =R c =R;

[0018] L x For phase winding, L in three-phase symmetrical winding a =L b =L c =L;

[0019] M is the mutual inductance, M ab =M ba =M bc =M cb =M ca =M ac =M;

[0020] S1.2, calculate the magnitude of the back electromotive force in the interval according to the received commutation signal;

[0021] Assuming that the interval commutation is from A+B-, that is, the current flows from the upper bridge arm of phase A into the lower bridge arm of phase B and out, to A+C-, that is, the upper bridge arm of phase A flows into the lower bridge arm of phase C and out, the three-phase terminal voltage equation is:

[0022]

[0023] Where U dc is the DC bus voltage. Since the commutation process lasts for a very short time, the value of the reverse electromotive force is assumed to remain unchanged, which is e a =-e b =-e c =E, combine the three equations:

[0024]

[0025] For the convenience of calculation, the commutation start time is t 0 , initial current i of phase winding a =-i b =I, the time domain expression of each phase current is:

[0026]

[0027] To reduce the electromagnetic torque pulsation, that is, to reduce the change rate of the B-phase current and the C-phase current, that is, have At this time, the back electromotive force must satisfy:

[0028] U dc =4E

[0029] S1.3, constructing a back electromotive force observer based on the received actual voltage and actual current;

[0030] Use i ab and U ab Line back electromotive force e ab For online observation, the motor terminal voltage equation is rewritten as:

[0031]

[0032] L ab is the equivalent inductance of AB phase winding, L ab =2(LM);

[0033] R ab is the equivalent resistance of AB phase winding, R ab =2R;

[0034] Observation matrix:

[0035]

[0036] K is the matrix gain coefficient,

[0037] The back EMF observation matrix is:

[0038]

[0039] As a further improvement of the modulation method of the present invention, the step S2 is specifically as follows:

[0040] S2.1. List the line back electromotive force equation according to the motor terminal voltage;

[0041] According to the motor model, the line back electromotive force equation is:

[0042]

[0043] The line back EMF lags the reverse EMF by 300, so the position where the line back EMF is zero is the switching moment. The line EMF zero crossing point is determined by the constructed line back EMF. At this moment, the inverter six-step state switching phase is performed, and the discrete switching phase moment signal is processed by phase-locked loop to obtain continuous rotor position information;

[0044] S2.2, perform voltage spike compensation in the low speed area on the detected rotor position;

[0045] When the inverter switches phases, the current in the inductor cannot change suddenly because the motor stator winding is inductive. When switching phases, the current will form a new loop through the anti-parallel diode of the MOSFET tube due to the shutdown of the original channel. At low speed, the heavier the load, the greater the winding current, and the longer the anti-parallel diode conduction time;

[0046]

[0047] t x is the on-time,

[0048] Calculate the conduction time t according to the motor parameters and operating conditions x , and then perform voltage spike compensation;

[0049] S2.3, perform voltage delay compensation in the high-speed zone for the detected rotor position;

[0050] At high speeds, the real-time requirements for the rotor position signal are higher, and the discrete signal will cause delays after passing through a low-pass filter, which has a greater impact at high speeds, so it is necessary to compensate for the signal delay;

[0051]

[0052] is the estimated speed, f LPF is the low-pass filter cutoff frequency, is the delay compensation angle.

[0053] As a further improvement of the modulation method of the present invention, the step S3 is specifically as follows:

[0054] S3.1, calculating the error value according to the received actual speed and the preset speed reference value;

[0055] Δω=ω ref -ω r

[0056] Among them, Δω is the error value, ω ref is the preset speed reference value, ω r is the actual speed;

[0057] S3.2, amplifying the error value according to a preset proportionality coefficient to obtain a first current value;

[0058] I out1 =K p-speed *Δω

[0059] Among them, I out1 is the first current value, K p-speed is the speed loop proportional coefficient;

[0060] S3.3, integrating the error value according to a preset integral coefficient to obtain a second current value;

[0061] I out2 =K i-speed *∫Δωdt

[0062] Among them, I out2 is the second current value, K i-speed is the speed loop integral coefficient;

[0063] S3.4, calculating a current reference value according to the first current value, the second current value and the amplitude limit value;

[0064] The current reference value is the sum of the first current value and the second current value, and the current is limited at the same time.

[0065] I ref =I out1 +I out2

[0066] Among them, I ref is the current reference value

[0067] S3.5, calculating the error value based on the received actual current and the current reference value;

[0068] ΔI=I ref -I real

[0069] Among them, ΔI is the error value, I ref To calculate the current reference value, I real is the actual current received;

[0070] S3.6, amplifying the error value according to a preset proportionality coefficient to obtain a first voltage value;

[0071] V out1 =K p-current *ΔI

[0072] Among them, V out1 is the first voltage value, K p-current is the preset proportional coefficient;

[0073] S3.7. Integrate the error value according to the received integral coefficient to obtain a second voltage value;

[0074] V out2 =K i-current *∫ΔIdt

[0075] Among them, V out2 is the second voltage value, K i-current is the preset integral coefficient;

[0076] S3.8, calculating the current loop output voltage reference value according to the first voltage value, the second voltage value and the amplitude limit value;

[0077] The DC bus voltage reference value is the sum of the first voltage value and the second voltage value, and the amplitude is limited at the same time.

[0078] V dc-ref =V out1 +V out2

[0079] Among them, V dc-ref is the DC bus voltage reference value.

[0080] As a further improvement of the modulation method of the present invention, the step S4 is specifically as follows:

[0081] S4.1. Derivation of the relationship between battery voltage and output voltage based on the working principle of four-switch buck-boost;

[0082] The four-switch buck-boost converter has a step-up and step-down function. If S1 and S3 are activated at the same time, and S2 and S4 are activated at the same time, then:

[0083] u dc =V in *D / (1-D)

[0084] Where D is the on-duty ratio of S1 and S3, V in is the power supply voltage;

[0085] S4.2, judging whether it is at the commutation moment according to whether the Hall signal is received, the DC bus voltage reference value at the non-commutation moment is the current loop output voltage reference value, and the DC bus voltage reference value at the commutation moment is the back electromotive force voltage;

[0086] At the commutation moment, in order to reduce the electromagnetic torque pulsation at the commutation moment, the DC bus voltage must be changed to meet U dc =4E, at the non-commutation moment, according to the control target and load characteristics, maintain the expected value U dc =V dc-ref ,

[0087]

[0088] S4.3, calculating the duty cycle according to the functional relationship between the DC bus voltage reference value and the four-switch buck-boost;

[0089] According to the relationship between the input voltage and the output voltage of the four-switch buck-boost converter, the modulation duty ratio D of the four-switch buck-boost at the switching moment and the non-switching moment is calculated;

[0090]

[0091] The actual DC bus voltage is sampled and fed back. Compared with the DC bus voltage reference value, if it is lower than the DC bus voltage, the duty cycle is increased. When the DC bus voltage is compared with the reference voltage, if the DC bus voltage is higher than the reference voltage, the duty cycle is reduced. The expected voltage is achieved through continuous convergence and approximation, and the actual output voltage is consistent.

[0092] As a further improvement of the modulation method of the present invention, in step S4, when the DC bus voltage is lower than the input voltage, S3 is kept normally closed and S4 is kept normally open. This topology is only used as a traditional BUCK. When the DC bus voltage is higher than the input voltage, S1 is kept normally closed and S2 is kept normally open. This topology is only used as a BOOST.

[0093] As a further improvement of the modulation method of the present invention, the step S5 is specifically as follows:

[0094] S5.1, judging the current sector position of the motor rotor according to the received rotor position signal;

[0095] According to the traditional six-step commutation method of brushless DC motor control, the entire interval is first divided into six sectors according to the received rotor position signal, each sector has an electrical angle of 60°, and in each sector only two phases are turned on, and the other phase is left floating;

[0096] S5.2, determining the three-phase conduction sequence according to the received rotor position information and the optimal commutation logic;

[0097] Assume that the rotor position signal received at this time is 60°. If the motor rotates clockwise, the AB phase should be turned on, and the current flows in from the B phase and out from the A phase. The next moment, if the rotor position signal received is 30°, the BC phase should be turned on, and the current flows in from the B phase and out from the C phase. The synthetic flux vector and the rotor flux vector are always kept between 60° and 120°, so as to ensure the maximum output torque.

[0098] S5.3, determine the on-off state of the three-phase bridge arm according to the optimal three-phase conduction sequence;

[0099] When the rotor position signal is 60°, the current flows in from phase B and out from phase A. PAM modulation is used to keep the upper bridge arm of phase B and the lower bridge arm of phase A normally open, and other switch tubes normally closed. The voltage and speed regulation are completed by the front-stage four-switch buck-boost. The three-phase inverter plays an electronic commutation function. As the speed increases or decreases, the time the rotor passes through the sector increases or decreases, which is reflected in the frequency, that is, the modulation frequency of the three-phase inverter changes accordingly with the change of speed.

[0100] The present invention provides a motor drive control method for a four-switch buck-boost motor based on a fuel cell, characterized in that the motor drive control method comprises:

[0101] First, the sampling circuit collects phase current, phase voltage and motor parameters, and receives rotor position information;

[0102] Then, according to the 2:2 conduction control method of the brushless DC motor, the angle between the synthetic magnetic flux and the rotor magnetic flux is always kept between 60° and 120°, and the optimal commutation position and commutation logic are determined to ensure the maximum output torque;

[0103] Secondly, in order to further suppress the electromagnetic torque pulsation caused by the anti-parallel diode of the inverter bridge arm when the winding current cannot change suddenly when switching phases, the overlapping commutation technology is added to the control, that is, when switching phases, the phase out is kept open, and the phase in is normally turned on according to the optimal commutation logic. Within the time of Δt, the three phases of the inverter are all in the open state;

[0104] Finally, since the overlapping conduction time Δt is affected by corresponding factors, including speed, load and parameters, the calculation is complicated. Therefore, it is proposed to adopt current zero-crossing detection technology, use hardware detection method to accurately judge the moment when the phase current is zero, turn off the phase and cycle according to the optimal commutation logic.

[0105] Compared with the prior art, the present invention proposes a four-switch buck-boost motor PAM modulation method and control method based on a fuel cell. The four-switch buck-boost BLDCM PAM modulation method for suppressing electromagnetic torque pulsation of a brushless DC motor is based on motor parameters and the actual current and actual voltage received to construct a back electromotive force observer, obtain the back electromotive force of the brushless DC motor in real time, obtain the rotor position based on the actual voltage and actual current information received, and then calculate the current reference value based on the actual speed received and the preset speed reference value, calculate the DC bus voltage reference value based on the actual current received and the current reference value, and then calculate the duty cycle D of the four-switch buck-boost based on the actual power supply voltage received and the DC bus voltage reference value, and finally determine the PAM modulation frequency based on the actual speed received. When the brushless DC motor works in the non-commutation area, the motor operation is controlled by the four-switch buck-boost voltage regulation. When the brushless DC motor works in the commutation area, the DC bus voltage is quickly adjusted so that U dc =4E, and at the same time, the switching phase is delayed to be turned off at the phase switching moment, so as to reduce the inconsistency between the current change rate of the switching phase and the switching phase, thereby reducing the electromagnetic torque pulsation during the operation of the brushless DC motor. When the actual speed of the motor is low, the PAM modulation frequency is low, and when the actual speed of the motor is high, the PAM modulation frequency is high. The PAM modulation frequency is consistent with the actual speed, which reduces the number of switching actions of the three-phase inverter switch tube and reduces the switching loss. It can improve the efficiency of the drive control system and improve the stability and robustness of the brushless DC motor drive system. BRIEF DESCRIPTION OF THE DRAWINGS

[0106] Figure 1 A driving circuit diagram of a PAM modulation strategy of a four-switch buck-boost BLDCM according to an example of the present invention;

[0107] Figure 2 A specific control block diagram of the back electromotive force observer of the present invention;

[0108] Figure 3 It is a specific flow chart of the speed-current dual closed-loop control system of an example of the present invention;

[0109] Figure 4 A specific flow chart of a four-switch buck-boost regulating DC bus voltage according to an example of the present invention;

[0110] Figure 5 It is a six-step commutation rotor position signal interval diagram of an example of the present invention;

[0111] Figure 6 This is a brushless DC motor drive control block diagram of an example of the present invention;

[0112] Figure 7 To simulate the three-phase current waveform of a traditional brushless DC motor in MATLAB / Simulink;

[0113] Figure 8 The three-phase current waveform diagram of the PAM modulation strategy of the BLDCM with four switches buck-boost simulated in MATLAB / Simulink of the present invention. DETAILED DESCRIPTION

[0114] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments:

[0115] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0116] The embodiment of the present invention provides a four-switch buck-boost motor PAM modulation method and control method based on a fuel cell, which are specifically as follows:

[0117] Step S1, constructing a back electromotive force observer according to the motor parameters and the actual current and voltage received, and obtaining the back electromotive force of the brushless DC motor in real time;

[0118] refer to Figure 2 is a specific control block diagram of step S1, step S1 includes:

[0119] S1.1. Construct the motor terminal voltage equation based on the motor model;

[0120]

[0121] u x is the phase voltage, and the subscript x represents the three-phase winding A, B, and C;

[0122] i x is the phase current;

[0123] u N is the voltage between the neutral point of the motor and the ground;

[0124] R x is the phase resistance, R in the three-phase symmetrical winding A =R B =R C =R;

[0125] L x For phase winding, L in three-phase symmetrical winding A =L B =L C =R;

[0126] M is the mutual inductance, M ab=M ba =M bc =M cb =M ca =M ac =M;

[0127] S1.2, calculate the magnitude of the back electromotive force in the interval according to the received commutation signal;

[0128] Assuming that the interval commutation is switched from A+B- (current flows from the upper bridge arm of phase A into the lower bridge arm of phase B and out) to A+C- (current flows from the upper bridge arm of phase A into the lower bridge arm of phase C and out), the three-phase terminal voltage equation is:

[0129]

[0130] Where U dc is the DC bus voltage. Since the commutation process lasts for a very short time, the value of the back electromotive force is assumed to remain unchanged, which is e a =-e b =-e c =E, combine the three equations:

[0131]

[0132] For the convenience of calculation, the commutation start time is t 0 ; The time domain expression of each phase current is:

[0133]

[0134] To reduce the electromagnetic torque pulsation, that is, to reduce the change rate of the B-phase current and the C-phase current, that is, have At this time, the back electromotive force must satisfy:

[0135] U dc =4E (5)

[0136] S1.3, constructing a back electromotive force observer based on the received actual voltage and actual current;

[0137] Use i ab and U ab Line back electromotive force e ab For online observation, the motor terminal voltage equation can be rewritten as:

[0138]

[0139] L ab is the equivalent inductance of AB phase winding, L ab =2(LM);

[0140] R ab is the equivalent resistance of AB phase winding, Rab =2R;

[0141] The observation matrix can be constructed:

[0142]

[0143] K is the matrix gain coefficient,

[0144] The back electromotive force observation matrix can be obtained as:

[0145]

[0146] Step 2: Based on the received actual voltage and actual current information, the step of estimating the rotor position includes:

[0147] S2.1. List the line back electromotive force equation according to the motor terminal voltage;

[0148] According to the motor model, the line back electromotive force equation is:

[0149]

[0150] The line back EMF lags the reverse EMF by 30°, so the position where the line back EMF is zero is the phase switching moment. Through the constructed line back EMF, the line EMF zero crossing point can be accurately known, and the inverter six-step state switching phase is performed at this moment. At the same time, the discrete switching phase moment signal is processed by the phase-locked loop to obtain continuous rotor position information.

[0151] S2.2, perform voltage spike compensation in the low speed area on the detected rotor position;

[0152] When the inverter switches phases, the current in the inductor cannot change suddenly because the motor stator winding is inductive. When switching phases, the original channel is turned off and the current forms a new loop through the anti-parallel diode of the MOSFET tube. At low speed, the heavier the load, the greater the winding current and the longer the anti-parallel diode is turned on.

[0153]

[0154] t x is the on-time,

[0155] Calculate the conduction time t according to the motor parameters and operating conditions x , and then perform voltage spike compensation;

[0156] S2.3, perform voltage delay compensation in the high-speed zone for the detected rotor position;

[0157] At high speeds, the real-time requirements for the rotor position signal are higher, and the discrete signal will cause delay when passing through the low-pass filter, which has a greater impact at high speeds, so the signal needs to be delayed.

[0158]

[0159] is the estimated speed, f LPF is the low-pass filter cutoff frequency, is the delay compensation angle;

[0160] Step 3: Calculate the current reference value based on the received actual speed and the preset speed reference value, and calculate the DC bus voltage reference value based on the received actual current and the current reference value:

[0161] See also Figure 3 , realize the double closed-loop control system of brushless DC motor, the specific steps are:

[0162] S3.1, calculating the error value according to the received actual speed and the preset speed reference value;

[0163] Δω=ω ref -ω r (12)

[0164] Among them, Δω is the error value, ω ref is the preset speed reference value, ω r is the actual speed.

[0165] S3.2, amplifying the error value according to a preset proportionality coefficient to obtain a first current value;

[0166] I out1 =K p-speed *Δω (13)

[0167] Among them, I out1 is the first current value, K p-speed is the speed loop proportional coefficient;

[0168] S3.3, integrating the error value according to a preset integral coefficient to obtain a second current value;

[0169] I out2 =K i-speed *∫Δωdt (14)

[0170] Among them, I out2 is the second current value, K i-speed is the speed loop integral coefficient;

[0171] S3.4, calculating a current reference value according to the first current value, the second current value and the amplitude limit value;

[0172] The current reference value is the sum of the first current value and the second current value, and the current is limited at the same time.

[0173] I ref =I out1 +I out2 (15)

[0174] Among them, I ref is the current reference value

[0175] S3.5, calculating the error value based on the received actual current and the current reference value;

[0176] ΔI=I ref -I real (16)

[0177] Among them, ΔI is the error value, I ref To calculate the current reference value, I real is the actual current received;

[0178] S3.6, amplifying the error value according to a preset proportionality coefficient to obtain a first voltage value;

[0179] V out1 =K p-current *ΔI (17)

[0180] Among them, V out1 is the first voltage value, K p-current is the preset proportional coefficient;

[0181] S3.7. Integrate the error value according to the received integral coefficient to obtain a second voltage value;

[0182] V out2 =K i-current *∫ΔIdt (18)

[0183] Among them, V out2 is the second voltage value, K i-current is the preset integral coefficient;

[0184] S3.8, calculating the current loop output voltage reference value according to the first voltage value, the second voltage value and the amplitude limit value;

[0185] The DC bus voltage reference value is the sum of the first voltage value and the second voltage value, and the amplitude is limited at the same time.

[0186] V dc-ref =V out1 +V out2 (19)

[0187] Among them, V dc-ref is the DC bus voltage reference value;

[0188] Step 4: Calculate the duty cycle D of the four-switch buck-boost according to the received actual power supply voltage and the DC bus voltage reference value. Step 4 includes:

[0189] S4.1. Derivation of the relationship between battery voltage and output voltage based on the working principle of four-switch buck-boost;

[0190] The four-switch buck-boost converter can realize the buck-boost function. If S1 and S3 are activated at the same time, and S2 and S4 are activated at the same time, then:

[0191] u dc =V in *D / (1-D) (20)

[0192] Where D is the on-duty ratio of S1 and S3, V in is the power supply voltage;

[0193] S4.2, judging whether it is at the commutation moment according to whether the Hall signal is received, the DC bus voltage reference value at the non-commutation moment is the current loop output voltage reference value, and the DC bus voltage reference value at the commutation moment is the back electromotive force voltage;

[0194] At the commutation moment, in order to reduce the electromagnetic torque pulsation at the commutation moment, the DC bus voltage must be changed to meet U dc =4E, at the non-commutation moment, according to the control target and load characteristics, maintain the expected value U dc =V dc-ref ,

[0195]

[0196] S4.3, calculating the duty cycle according to the functional relationship between the DC bus voltage reference value and the four-switch buck-boost;

[0197] According to the relationship between the input voltage and the output voltage of the four-switch buck-boost converter, the modulation duty ratio D of the four-switch buck-boost at the switching moment and the non-switching moment is calculated.

[0198]

[0199] Please refer to Figure 4 , sample and feedback the actual DC bus voltage, and compare it with the DC bus voltage reference value. If it is lower than the DC bus voltage, increase the duty cycle. When comparing the DC bus voltage with the reference voltage, if the DC bus voltage is higher than the reference voltage, reduce the duty cycle. Through continuous convergence and approximation, the expected voltage is consistent with the actual output voltage.

[0200] In addition, in order to further improve the efficiency of the DC / DC topology, when the DC bus voltage is lower than the input voltage, S3 is kept normally closed and S4 is kept normally open. This topology is only used as a traditional BUCK. When the DC bus voltage is higher than the input voltage, S1 is kept normally closed and S2 is kept normally open. This topology is only used as a BOOST.

[0201] Step 5: Determine the PAM modulation frequency based on the actual speed received:

[0202] First, analyze the PAM modulation principle:

[0203] like Figure 1 The three-phase voltage inverter circuit shown in the figure has a load phase voltage U UN , U VN , U WN It can be obtained by the following formula:

[0204]

[0205] The three formulas can be combined to get:

[0206]

[0207] The motor winding is an inductive load. The larger the inductance, the larger the load impedance angle, the current cannot change suddenly and the longer the continuous current time. Expand the output line voltage into a Fourier series to get:

[0208]

[0209] n=6k±1, k is a natural number;

[0210] The effective value of the output line voltage is:

[0211]

[0212] The output phase voltage is expanded into Fourier series:

[0213]

[0214] n=6k±1, k is a natural number;

[0215] The effective value of the output phase voltage is:

[0216]

[0217] Step 5: Specific practical steps include:

[0218] S5.1, judging the current sector position of the motor rotor according to the received rotor position signal;

[0219] According to the traditional six-step commutation method of brushless DC motor control, the entire interval is first divided into six sectors based on the received rotor position signal, each sector has an electrical angle of 60°, and in each sector only two phases are turned on, and the other phase is left floating.

[0220] S5.2, determining the three-phase conduction sequence according to the received rotor position information and the optimal commutation logic;

[0221] Please see Figure 5 , assuming that the rotor position signal received at this time is 60°. The motor rotates clockwise, then the AB phases should be turned on, the current flows into the B phase and flows out of the A phase. The next moment, the rotor position signal received is 30°, then the BC phase should be turned on, the current flows into the B phase and flows out of the C phase, always keeping the synthetic flux vector and the rotor flux vector between 60°-120°, so as to ensure the maximum output torque.

[0222] S5.3, determine the on-off state of the three-phase bridge arm according to the optimal three-phase conduction sequence;

[0223] When the rotor position signal is 60°, it can be seen that the current flows in from phase B and out from phase A. PAM modulation is used to keep the upper bridge arm of phase B and the lower bridge arm of phase A normally open, and other switches are normally closed. The voltage and speed regulation are completed by the four-switch buck-boost in the front stage, and the three-phase inverter plays an electronic commutation function. As the speed increases or decreases, the time the rotor passes through the sector increases or decreases, which is reflected in the frequency, that is, the modulation frequency of the three-phase inverter changes accordingly with the change of the speed.

[0224] At the same time, overlapping commutation technology is added to suppress electromagnetic torque pulsation at the moment of phase switching of the brushless DC motor. That is, at the moment of phase switching, the phase to be switched out is turned off with delay. During this Δt time, all three phases are turned on, and the moment of current zero crossing is detected by hardware to determine the relevant switching off moment. Due to the use of hardware detection, there is no need to calculate the delayed on-time Δt in real time, which reduces the amount of calculation and is more accurate and timely.

[0225] For the block diagram of the brushless DC motor drive control system, please see Figure 6 , the control method is used for simulation verification. When the traditional six-step commutation drive control method of brushless DC motor is adopted, the simulation results are as follows Figure 7 As shown in Figure 1, it can be seen that the electromagnetic torque has large fluctuations. At the commutation moment, the pulsating electromagnetic torque can even exceed the normal torque by more than 50%. The PAM modulation of the BLDCM with four-switch buck-boost is adopted. The simulation results are shown in Figure 1. Figure 8 As shown, it can be seen that changing the DC bus voltage and adopting the commutation overlap method can reduce the electromagnetic torque pulsation caused by the inability of the phase winding commutation current to change suddenly, improve the system operation efficiency, and expand the application of brushless DC motors in the field of hydrogen fuel cell air compressors.

[0226] The above description is only a preferred embodiment of the present invention and does not constitute any other form of limitation to the present invention. Any modification or equivalent change made based on the technical essence of the present invention still falls within the scope of protection required by the present invention.

Claims

1. A four-switch buck-boost motor PAM modulation method based on a fuel cell, the specific steps are as follows, characterized in that: S1. According to the brushless motor parameters and the actual current and voltage received, a back electromotive force observer is constructed to obtain the back electromotive force of the brushless DC motor in real time. The step S1 is specifically as follows: S1.

1. Construct the motor terminal voltage equation based on the motor model; u x is the phase voltage, and the subscript x represents the three-phase winding a, b, and c; i x is the phase current; e x is the opposite electromotive force; u N is the voltage between the neutral point of the motor and the ground; R x is the phase resistance, R in the three-phase symmetrical winding a =R b =R c =R; L x For phase winding, L in three-phase symmetrical winding a =L b =L c =L; M is the mutual inductance, M ab =M ba =M bc =M cb =M ca =M ac =M; S1.2, calculate the magnitude of the back electromotive force in the interval according to the received commutation signal; Assuming that the interval commutation is from A+B-, that is, the current flows from the upper bridge arm of phase A into the lower bridge arm of phase B and out, to A+C-, that is, the upper bridge arm of phase A flows into the lower bridge arm of phase C and out, the three-phase terminal voltage equation is: Where U dc is the DC bus voltage. Since the commutation process lasts for a very short time, the value of the reverse electromotive force is assumed to remain unchanged, which is e a =-e b =-e c =E, combine the three equations: For the convenience of calculation, the starting time of commutation is t0, and the initial current of the phase winding is i a =-i b =I, the time domain expression of each phase current is: To reduce the electromagnetic torque pulsation, that is, to reduce the change rate of the B-phase current and the C-phase current, that is, have At this time, the back electromotive force must satisfy: IN dc =4E S1.3, constructing a back electromotive force observer based on the received actual voltage and actual current; Use i ab and U ab Line back electromotive force e ab For online observation, the motor terminal voltage equation is rewritten as: L ab is the equivalent inductance of AB phase winding, L ab =2(LM); R ab is the equivalent resistance of AB phase winding, R ab =2R; Observation matrix: K is the matrix gain coefficient, The back EMF observation matrix is: S2, estimating the rotor position based on the received actual voltage and actual current information; S3, calculating a current reference value according to the received actual speed and a preset speed reference value, and calculating a DC bus voltage reference value according to the received actual current and the current reference value; The step S3 is specifically as follows: S3.1, calculating the error value based on the received actual speed and the preset speed reference value; Give = oh ref -oh r Among them, Δω is the error value, ω ref is the preset speed reference value, ω r is the actual speed; S3.2, amplifying the error value according to a preset proportionality coefficient to obtain a first current value; I out1 =K p-speed *See Among them, I out1 is the first current value, K p-speed is the speed loop proportional coefficient; S3.3, integrating the error value according to a preset integral coefficient to obtain a second current value; I out2 =K i-speed *∫Δωdt Among them, I out2 is the second current value, K i-speed is the speed loop integral coefficient; S3.4, calculating a current reference value according to the first current value, the second current value and the amplitude limit value; The current reference value is the sum of the first current value and the second current value, and the current is limited at the same time. I ref =I out1 +I out2 Among them, I ref is the current reference value S3.5, calculating the error value based on the received actual current and the current reference value; ΔI=I ref -I real Among them, ΔI is the error value, I ref To calculate the current reference value, I real is the actual current received; S3.6, amplifying the error value according to a preset proportionality coefficient to obtain a first voltage value; V out1 =K p-current *ΔI Among them, V out1 is the first voltage value, K p-current is the preset proportional coefficient; S3.

7. Integrate the error value according to the received integral coefficient to obtain a second voltage value; V out2 =K i-current *∫ΔIdt Among them, V out2 is the second voltage value, K i-current is the preset integral coefficient; S3.8, calculating the current loop output voltage reference value according to the first voltage value, the second voltage value and the amplitude limit value; The DC bus voltage reference value is the sum of the first voltage value and the second voltage value, and the amplitude is limited at the same time. V dc-ref =V out1 +V out2 Among them, V dc-ref is the DC bus voltage reference value; S4, calculating the duty cycle D of the four-switch buck-boost according to the received actual power supply voltage and the DC bus voltage reference value; The step S4 is specifically as follows: S4.

1. Derivation of the relationship between battery voltage and output voltage based on the working principle of four-switch buck-boost; The four-switch buck-boost converter has a step-up and step-down function. If S1 and S3 are activated at the same time, and S2 and S4 are activated at the same time, then: u dc =V in *D(1-D) Where D is the on-duty ratio of S1 and S3, V in is the power supply voltage; S4.2, judging whether it is at the commutation moment according to whether the Hall signal is received, the DC bus voltage reference value at the non-commutation moment is the current loop output voltage reference value, and the DC bus voltage reference value at the commutation moment is the back electromotive force voltage; At the commutation moment, in order to reduce the electromagnetic torque pulsation at the commutation moment, the DC bus voltage must be changed to meet U dc =4E, at the non-commutation moment, according to the control target and load characteristics, maintain the expected value U dc =V dc-ref , S4.3, calculating the duty cycle according to the functional relationship between the DC bus voltage reference value and the four-switch buck-boost; According to the relationship between the input voltage and the output voltage of the four-switch buck-boost converter, the modulation duty ratio D of the four-switch buck-boost at the switching moment and the non-switching moment is calculated; The actual DC bus voltage is sampled and fed back. If it is lower than the DC bus voltage reference value, the duty cycle is increased. If the DC bus voltage is higher than the reference voltage, the duty cycle is reduced. The expected voltage is consistent with the actual output voltage through continuous convergence and approximation. S5, determining the PAM modulation frequency according to the received actual rotation speed; The step S5 is specifically as follows: S5.1, judging the current sector position of the motor rotor according to the received rotor position signal; According to the traditional six-step commutation method of brushless DC motor control, the entire interval is first divided into six sectors according to the received rotor position signal, each sector has an electrical angle of 60°, and in each sector only two phases are turned on, and the other phase is left floating; S5.2, determining the three-phase conduction sequence according to the received rotor position information and the optimal commutation logic; Assume that the rotor position signal received at this time is 60°. If the motor rotates clockwise, the AB phase should be turned on, and the current flows in from the B phase and out from the A phase. The next moment, if the rotor position signal received is 30°, the BC phase should be turned on, and the current flows in from the B phase and out from the C phase. The synthetic flux vector and the rotor flux vector are always kept between 60° and 120°, so as to ensure the maximum output torque. S5.3, determine the on-off state of the three-phase bridge arm according to the optimal three-phase conduction sequence; When the rotor position signal is 60°, the current flows in from phase B and out from phase A. PAM modulation is used to keep the upper bridge arm of phase B and the lower bridge arm of phase A normally open, and other switch tubes normally closed. The voltage and speed regulation are completed by the front-stage four-switch buck-boost. The three-phase inverter plays an electronic commutation function. As the speed increases or decreases, the time the rotor passes through the sector increases or decreases, which is reflected in the frequency, that is, the modulation frequency of the three-phase inverter changes accordingly with the change of speed.

2. The four-switch buck-boost motor PAM modulation method based on fuel cell according to claim 1, characterized in that: The step S2 is specifically as follows: S2.

1. List the line back electromotive force equation according to the motor terminal voltage; According to the motor model, the line back electromotive force equation is: The line back EMF lags the reverse EMF by 30°, so the position where the line back EMF is zero is the switching moment. The line back EMF zero crossing point is determined by the constructed line back EMF. At this moment, the inverter six-step state switching phase is performed, and the discrete switching phase moment signal is processed by phase-locked loop to obtain continuous rotor position information; S2.2, perform voltage spike compensation in the low speed area on the detected rotor position; When the inverter switches phases, the current in the inductor cannot change suddenly because the motor stator winding is inductive. When switching phases, the current will form a new loop through the anti-parallel diode of the MOSFET tube due to the shutdown of the original channel. At low speed, the heavier the load, the greater the winding current, and the longer the anti-parallel diode conduction time; t x is the on-time, Calculate the conduction time t according to the motor parameters and operating conditions x , and then perform voltage spike compensation; S2.3, perform voltage delay compensation in the high-speed zone for the detected rotor position; At high speeds, the real-time requirements for the rotor position signal are higher, and the discrete signal will cause delays after passing through a low-pass filter, which has a greater impact at high speeds, so it is necessary to compensate for the signal delay; is the estimated speed, f LPF is the low-pass filter cutoff frequency, is the delay compensation angle.

3. The four-switch buck-boost motor PAM modulation method based on fuel cell according to claim 1, characterized in that: In step S4, when the DC bus voltage is lower than the input voltage, S3 is kept normally closed and S4 is kept normally open. This topology is only used as a traditional BUCK. When the DC bus voltage is higher than the input voltage, S1 is kept normally closed and S2 is kept normally open. This topology is only used as a BOOST.

4. The four-switch buck-boost motor PAM modulation method based on a fuel cell according to any one of claims 1 to 3, characterized in that: The motor drive control method comprises: First, the sampling circuit collects phase current, phase voltage and motor parameters, and receives rotor position information; Then, according to the 2:2 conduction control method of the brushless DC motor, the angle between the synthetic flux and the rotor flux is always kept between 60° and 120°, and the optimal commutation position and commutation logic are determined to ensure the maximum output torque. Secondly, in order to further suppress the electromagnetic torque pulsation caused by the anti-parallel diode of the inverter bridge arm when the winding current cannot change suddenly when switching phases, the overlapping commutation technology is added to the control, that is, when switching phases, the phase out is kept open, and the phase in is normally turned on according to the optimal commutation logic. Within the time of Δt, the three phases of the inverter are all in the open state; Finally, since the overlapping conduction time Δt is affected by corresponding factors, including speed, load and parameters, the calculation is complicated. Therefore, it is proposed to adopt current zero-crossing detection technology, use hardware detection method to accurately judge the moment when the phase current is zero, turn off the phase and cycle according to the optimal commutation logic.

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