Brushless direct current motor driving circuit and analysis method thereof

Abstract

The invention discloses a brushless direct current motor driving circuit, which comprises a three-phase bridge arm circuit with six MOS (Metal Oxide Semiconductor) tubes, a grid electrode of each MOS tube is connected with a compensation capacitor and charge discharge resistor module and a capacitor charge and discharge resistor module, and a switching pulse absorption RC (Resistance-Capacitance) module is connected between a source electrode and a drain electrode of each MOS tube; the compensation capacitor and charge bleeder resistor module comprises a compensation capacitor and a charge bleeder resistor connected in parallel with the compensation capacitor; the capacitor charge-discharge resistor module comprises a first charge-discharge resistor, a second charge-discharge resistor and a diode, and the second charge-discharge resistor is connected with the diode in series and then connected with the first charge-discharge resistor in parallel. According to the circuit design, the risk of current leakage between the upper arm and the lower arm of the three-phase bridge arm circuit can be prevented, and the probability of ringing effect of the MOS tube can be reduced; and through analysis of a brushless direct current motor driving circuit, an analysis process from design requirements to circuit realization is completed, and demonstration is carried out aiming at vehicle gauge electrical interference and circuit design parameters.

Description

Technical Field

[0001] The present invention relates to the technical field of brushless DC motors, and more specifically, to a brushless DC motor drive circuit and an analysis method thereof. Background Art

[0002] Research on brushless DC motors is now the trend of the times. Brushless DC motors have advantages in life and speed due to their lack of mechanical steering gear. Therefore, their share in the field of motor applications is gradually increasing. In particular, brushless DC motors have already taken a dominant position in new energy vehicles and aircraft.

[0003] The requirements for brushless DC motor control circuits are gradually increasing. The mainstream brushless motor control circuit adopts a three-phase bridge arm (6MOS) structure, but different design manufacturers use different modes for motor control, such as 6-step square wave, magnetic field vector control, etc., all for achieving high-efficiency control at low cost. At the same time, higher requirements are also put forward for electrical compatibility and electrical performance.

[0004] Innovation in brushless DC motor control circuits is a market competitiveness. With the popularity of new energy electric vehicles and the widespread use of brushless DC motors, the auto parts industry itself is highly competitive; therefore, the control design of brushless DC motors is constantly being innovated. Summary of the invention

[0005] The present invention overcomes the shortcomings of the prior art and provides a brushless DC motor drive circuit. The circuit design can prevent the risk of leakage current between the upper and lower arms of the three-phase bridge arm circuit and reduce the probability of ringing effect of the MOS tube.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A brushless DC motor drive circuit comprises a three-phase bridge arm circuit with six MOS tubes, the gate of each MOS tube is connected to a compensation capacitor and a charge discharge resistor module and a capacitor charge and discharge resistor module, and a switch pulse absorption RC module is connected between the source and drain of each MOS tube.

[0008] Preferably, the compensation capacitor and charge discharge resistor module includes a compensation capacitor and a charge discharge resistor connected in parallel with the compensation capacitor.

[0009] Preferably, the capacitor charge and discharge resistor module includes a first charge and discharge resistor, a second charge and discharge resistor and a diode, and the second charge and discharge resistor and the diode are connected in series and then in parallel with the first charge and discharge resistor.

[0010] Preferably, the switch pulse absorption RC module includes a pulse absorption resistor and a pulse absorption capacitor connected in parallel between the source and drain of the MOS tube, and the pulse absorption resistor and the pulse absorption capacitor are connected in series.

[0011] Preferably, both ends of each phase winding of the brushless DC motor are connected in parallel with a correction capacitor.

[0012] Preferably, it also includes a port capacitor with one end connected to the winding and the other end grounded.

[0013] Preferably, a reverse voltage acquisition module is also included, and the reverse voltage acquisition module includes a first acquisition resistor, a second acquisition resistor and a acquisition capacitor connected to the winding, and the acquisition capacitor is connected in parallel with the second acquisition resistor.

[0014] The present invention also provides an analysis method for the brushless DC motor drive circuit as described above, comprising the following steps:

[0015] S1. Analysis of magnetic field vector control of brushless DC motor;

[0016] S2. Electric power analysis of the motor in the brushless DC motor drive circuit;

[0017] S3. Selection analysis of MOS tubes in brushless DC motor drive circuits;

[0018] S4. Analysis of gate drive circuit of MOS tube in brushless DC motor drive circuit;

[0019] S5. Analysis of RC absorption circuit in brushless DC motor drive circuit;

[0020] S6. Analysis of power correction circuit in brushless DC motor drive circuit;

[0021] S7. Analysis of drive line conduction emission containment in brushless DC motor drive circuit;

[0022] S8. Analysis of power line conducted emission containment in brushless DC motor drive circuit;

[0023] S9. Analysis of radiated emissions in brushless DC motor drive circuits.

[0024] Beneficial effects of the present invention:

[0025] The circuit design of the present invention can prevent the risk of leakage current between the upper and lower arms of the three-phase bridge arm circuit, and can reduce the probability of ringing effect in the MOS tube; and through the analysis of the brushless DC motor drive circuit, the analysis process from design requirements to circuit implementation is completed, and the design parameters of the circuit are demonstrated for vehicle-standard electrical interference. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a structural schematic diagram of a brushless DC motor driving circuit according to a specific embodiment of the present invention;

[0027] Figure 2A schematic diagram of the connection structure between the coil winding and the inside of the coil according to a specific embodiment of the present invention;

[0028] Figure 3 The specific embodiment of the present invention reflects Figure 2 Vector diagram of magnetic force;

[0029] Figure 4 The specific embodiment of the present invention reflects Figure 3 The process of vector diagram analysis;

[0030] Figure 5 A hexagonal vector diagram of a specific embodiment of the present invention;

[0031] Figure 6 The specific embodiment of the present invention reflects Figure 5 The process of analyzing the hexagonal vector diagram;

[0032] Figure 7 The specific embodiment of the present invention reflects the electric power analysis process of the motor;

[0033] Figure 8 A waveform diagram of MOS gate voltage reflected in a specific embodiment of the present invention;

[0034] Fig. 9 This is a diagram showing the MOS gate drive waveform and harmonic spectrum according to a specific embodiment of the present invention;

[0035] Fig.10 Schematic diagram of device capacitance and parasitic capacitance according to a specific embodiment of the present invention Figure 1 ;

[0036] Fig.11 Schematic diagram of device capacitance and parasitic capacitance according to a specific embodiment of the present invention Figure 2 .

[0037] In the figure: 1. MOS tube; 2. Compensation capacitor and charge discharge resistor module; 3. Capacitor charge and discharge resistor module; 4. Switch pulse absorption RC module; 5. Correction capacitor; 6. Port capacitor; 7. Reverse voltage acquisition module. DETAILED DESCRIPTION

[0038] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] like Figure 1-11As shown, a brushless DC motor drive circuit includes a three-phase bridge arm circuit with six MOS tubes 1, the gate of each MOS tube 1 is connected to a compensation capacitor and charge discharge resistor module 2 and a capacitor charging and discharging resistor module 3, and a switch pulse absorption RC module 4 is connected between the source and the drain of each MOS tube 1; the compensation capacitor and charge discharge resistor module 2 includes a compensation capacitor and a charge discharge resistor connected in parallel with the compensation capacitor; the capacitor charging and discharging resistor module 3 includes a first charging and discharging resistor, a second charging and discharging resistor and a diode, and the second charging and discharging resistor and the diode are connected in series and then connected in parallel with the first charging and discharging resistor; the switch pulse absorption RC module 4 includes a pulse absorption resistor and a pulse absorption capacitor connected in parallel between the source and the drain of the MOS tube 1, and the pulse absorption resistor and the pulse absorption capacitor are connected in series; both ends of each phase winding of the brushless DC motor are connected in parallel with a correction capacitor 5; it also includes a port capacitor 6 with one end connected to the winding and the other end grounded; it also includes a reverse voltage acquisition module 7, the reverse voltage acquisition module 7 includes a first acquisition resistor, a second acquisition resistor and an acquisition capacitor connected to the winding, and the acquisition capacitor is connected in parallel with the second acquisition resistor.

[0040] Analysis of magnetic field vector control:

[0041] The structure of the brushless DC motor: the rotor can be composed of permanent magnets; the stator can be composed of circumferentially distributed slots and coils on the slots; the force that pushes the rotor comes from the interaction between the magnetic polarity generated on the coil and the polarity of the permanent magnet. When the coil is energized, a magnetic flux is formed (Φ=Li). Therefore, the vector of the magnetic flux is proportional to the vector of the current on the coil. From the connection structure of the coil inside the motor, we can know the direction of the magnetic field of each coil winding (three windings driven simultaneously), and from the motor manufacturing parameters, we can know that |Φx1|=|Φx2|. Because the controlled parameters in the circuit are expressed in current and voltage. The magnetic field distribution inside the motor can be represented by current and voltage vector diagrams.

[0042] From the vector diagram, we can see that the combined magnetic force that interacts with the permanent magnet rotor is generated in the direction of the synthetic vector. This combined magnetic force comes from the combined magnetic force generated in each phase pair direction. Under this magnetic force cooperation, the rotor will move in the direction of the synthetic vector, and the angle between the two will gradually decrease until they are parallel. That is, the rotor moves in the direction of the synthetic vector and the force is balanced.

[0043] The circuit for driving the brushless DC motor consists of three combined half bridges, each with two potential outputs. Therefore, there are 8 combinations. From the circuit drive, we can see that the combination of (111) and (000) has no driving effect. To visualize the overlap of the 8 controlled states and the motor motion angle, the following 6-angle vector diagram is obtained.

[0044] Since the drive circuit has only 8 output states, some of the 8 output states need to be synthesized to synthesize any vector. The 6-angle vector diagram has integrated the motor operation angle state and divided it into 6 module areas. Therefore, the vector synthesis theorem shows that the required control vector Um can be synthesized by the boundary vector of the area. That is, it is synthesized by the boundary state of the area where the drive circuit outputs, and each output state can occupy a different time within a fixed period T. In this way, the synthetic vector can rotate in the area.

[0045] Therefore, as long as the rotor angle θ is clear, the region can be known through the vector diagram, and the maintenance time of the boundary output state can be calculated. Thus, a controlled motor can be realized. The stator coil of the brushless DC motor is a Δ connection in which the three coil windings are connected end to end, or a Y connection in which the middle wire ends are connected. Considering the symmetry of the three-phase winding of the motor, it can be simplified to analyze the single-circuit coil mode. R is the resistance of a single coil, L is the inductance of a single-phase coil, and Ex is the reverse electromotive force.

[0046] For the electric power analysis of the motor in the brushless DC motor drive circuit:

[0047] The rotation angle θ of Um is the rotation angle of the motor rotor.

[0048] Um's It is the angular velocity of the motor rotor.

[0049] The value of |Um| can approximately linearly determine the motor torque when ω is constant.

[0050] Motor torque: T = R*F; Motor work: dW = T*dθ; Motor rotation angle: dθ = ωdt; Motor angular velocity: ω = 2πn;

[0051] Therefore, the motor does work: dW = T*2πndt; and then according to the power definition: P = T2πn;

[0052] Usually P is expressed in (kw) and n is expressed in (rev / min)

[0053] That is: P1000 = T * 2πn / 60;

[0054] From this we can get: P = T*n / 9550; if the mechanical conversion efficiency is η, then the electrical power is P / η.

[0055] Therefore, controlling the rotation of the brushless DC motor becomes Um, drawing circles of different radii on the vector diagram (E = |Um|e j θ ).

[0056] Selection analysis of MOS tubes in brushless DC motor drive circuits:

[0057] After the electric power of the motor is determined, the rated current of the motor coil can be calculated; at the same time, the impact current generated when the motor is stalled must also be considered.

[0058] If the motor power is P, then the power of each winding is (using magnetic field vector control mode), and the effective value of the winding voltage is

[0059] That is, the effective value of the winding current can be calculated as When the motor is stalled or started, the inrush current tends to Assume the internal resistance of the winding is r.

[0060] Therefore, it can be concluded that the electrical parameters of MOS are as follows:

[0061] Assume that the MOS on-resistance is Ron and the thermal resistance is RθJA (without external heat dissipation facilities).

[0062] Since the operating temperature of automotive products is often required to be 85℃ or 125℃, the upper limit of the junction temperature design of MOS is 150℃; therefore, the temperature rise needs to be controlled within 25℃. Consider the temperature rise limit and select the appropriate Ron.

[0063] Analysis of the gate drive circuit of the MOS tube in the brushless DC motor drive circuit:

[0064] Due to the existence of MOS inter-electrode capacitance and the internal bias electric field effect, there is a certain delay in the opening and closing of MOS. For example, in the driving circuit, there are two MOSs, one on the upper and one on the lower, in each half bridge. When the gate is driven by the same circuit, there is a crossover time between the upper and lower MOS. This will cause the risk of leakage current between the upper and lower arms. Therefore, different charging and discharging resistors of the gate capacitor are used to adjust the opening and closing time. During the opening process of MOS, DS crosses from cutoff to saturation conduction, and the capacitor between GD plays the effect of parallel connection to GS. As a result, the voltage of the G pole maintains a short period of slow rise. This process will cause problems such as MOS heating. Therefore, the gate compensation capacitor is used to alleviate this process. In addition, considering the risk of the gate capacitance being unable to discharge due to the shutdown of the driving circuit due to special circumstances, and also from the perspective of stability, a pull-down discharge resistor is connected in parallel.

[0065] Analysis of RC absorption circuit in brushless DC motor drive circuit:

[0066] Because MOS is in a periodic on-off process.

[0067]

[0068]

[0069] Special circumstances, when There are no even harmonics.

[0070] The above shows that when MOS is in periodic switching, harmonic components will be generated at both ends. The working current of the motor is the primary and secondary waves, and the remaining harmonics act on the driving circuit and will respond to the RLC parameters of the circuit itself. When the harmonics are switched, they will oscillate and decay, which is the ringing effect. Therefore, connecting RC in parallel between MOS and DS can appropriately delay the gradient of the MOS switching waveform, thereby compressing the bandwidth of the harmonic spectrum and reducing the probability of the harmonic ringing effect.

[0071] Analysis of power correction circuit in brushless DC motor drive circuit:

[0072] Since the winding coil of the motor has a large inductance and a certain internal resistance. The motor is connected to the drive circuit, and the three-phase bridge arm generates an alternating voltage to drive the motor. Driven by the alternating voltage, a sinusoidal current (main wave current) is generated on the coil winding. Due to the effect of the inductance, there is a certain phase difference between the driving voltage and the current, which causes the reactive power component to increase. Therefore, capacitors are connected in parallel at both ends of the winding to correct the impedance angle to reduce the proportion of reactive power.

[0073] Analysis of drive line conduction emission containment in brushless DC motor drive circuits:

[0074] Since the motor speed is limited, that is, the main wave frequency is not high, the frequency of each harmonic will not be too high. Therefore, the 2m wire harness can still be regarded as a short-line transmission in the experiment, and the lumped parameter circuit model can be used for analysis. From the above analysis, it can be obtained that there is a collective transmission of each harmonic on the wire harness. Therefore, the experimental equipment must measure the voltage division value of each harmonic component at the measuring end. In addition, due to the existence of RLC in the circuit structure, when the harmonic angular frequency When the voltage value of this component is measured, it is particularly large. If the experimental limit value of this frequency band is low, it will exceed the standard. If there is a margin for the experimental limit value in the high frequency band, the parasitic capacitance method can still be slightly changed. If the limit value is very tight, a three-phase common mode inductor can be used at the output end of the drive circuit. In addition, if the motor drive power is very large, although the frequency of the main wave is not high, the energy of the Nth harmonic is still very large. When the frequency rises to the 100-megahertz level, it is necessary to consider it according to the distributed parameters.

[0075] Analysis of conducted emission containment on power lines in brushless DC motor drive circuits:

[0076] When the motor starts, the current cannot be supplied quickly due to the inductance on the power supply; the power supply capacitor performs instantaneous compensation. The greater the energy storage of the capacitor, the smaller the supply voltage fluctuation on the drive circuit. Q = CΔU = It; ΔU is the effective value of the power supply fluctuation, I is the effective value of the motor starting current, and t is the starting time. Obviously, this capacitor needs to be very large, but considering the cost, the value of the capacitor is often limited. Therefore, the capacitor compensation current is limited and must ultimately be obtained from the power supply. The transient current is curbed by the inductance of the artificial network, and the capacitance flowing to the device is monitored by the measuring device. Since the built-in resistance of the measuring device is often 50Ω, when there is high-frequency harmonic current on the power line (to meet long-line transmission requirements); due to the characteristic impedance of the power line This often does not match the built-in resistance of the device, causing reflection of the transmitted signal, which in turn enhances the effect of radiated emissions.

[0077] For the analysis of radiated emission in brushless DC motor drive circuit:

[0078] As discussed above, when the harmonic components of the power supply fluctuations of the driving circuit meet the long-line transmission on the power line, the impedance mismatch will cause signal reflection, which will aggravate the effect of radiation emission. The power supply fluctuations of the driving circuit provide the signal source, and the power supply circuit bears the carrier of the antenna. The characteristic impedance of the circuit and the matching degree of the terminal load determine the efficiency of radiation emission. When the driving circuit is working, it often requires many high-frequency digital signals as control. Under the action of the control signal, the power device periodically switches. These effectively generate alternating signal sources. These signal sources propagate in their respective circuit loops, and each generates its own alternating magnetic flux in the loop during the transmission process. The mutual generation of electromagnetics causes it to propagate outward in the form of electromagnetic waves, causing radiation emission.

[0079] Therefore, when designing a circuit:

[0080] 1. Try to control the frequency and rising and falling gradients of digital signals to reduce harmonic frequency and harmonic bandwidth.

[0081] 2. The routing length should be as short as possible (the loop area should be as small as possible) to avoid long-line transmission effect.

[0082] 3. Achieve impedance matching and reduce reflection.

[0083] 4. If necessary, high-frequency signal routing should be designed in the inner pad layer to achieve a shielding effect.

[0084] 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 brushless DC motor drive circuit, comprising a three-phase bridge arm circuit having six MOS tubes (1), characterized in that: The gate of each MOS tube (1) is connected to a compensation capacitor and charge discharge resistor module (2) and a capacitor charge and discharge resistor module (3), and a switch pulse absorption RC module (4) is connected between the source and drain of each MOS tube (1).

2. A brushless DC motor drive circuit according to claim 1, characterized in that: The compensation capacitor and charge discharge resistor module (2) comprises a compensation capacitor and a charge discharge resistor connected in parallel with the compensation capacitor.

3. A brushless DC motor drive circuit according to claim 2, characterized in that: The capacitor charging and discharging resistor module (3) comprises a first charging and discharging resistor, a second charging and discharging resistor and a diode. The second charging and discharging resistor and the diode are connected in series and then in parallel with the first charging and discharging resistor.

4. A brushless DC motor drive circuit according to claim 3, characterized in that: The switch pulse absorption RC module (4) comprises a pulse absorption resistor and a pulse absorption capacitor connected in parallel between the source and drain of the MOS tube (1), and the pulse absorption resistor and the pulse absorption capacitor are connected in series.

5. A brushless DC motor drive circuit according to any one of the preceding claims, characterized in that: Both ends of each phase winding of the brushless DC motor are connected in parallel with a correction capacitor (5).

6. A brushless DC motor drive circuit according to claim 5, characterized in that: It also includes a terminal capacitor (6) with one end connected to the winding and the other end grounded.

7. A brushless DC motor drive circuit according to claim 6, characterized in that: It also includes a reverse voltage acquisition module (7), which includes a first acquisition resistor, a second acquisition resistor and a acquisition capacitor connected to the winding, and the acquisition capacitor is connected in parallel with the second acquisition resistor.

8. An analysis method for a brushless DC motor drive circuit as claimed in claim 1, characterized in that: The following steps are involved: S1. Analysis of magnetic field vector control of brushless DC motor; S2. Electric power analysis of the motor in the brushless DC motor drive circuit; S3. Selection analysis of MOS tubes in brushless DC motor drive circuits; S4. Analysis of gate drive circuit of MOS tube in brushless DC motor drive circuit; S5. Analysis of RC absorption circuit in brushless DC motor drive circuit; S6. Analysis of power correction circuit in brushless DC motor drive circuit; S7. Analysis of drive line conduction emission containment in brushless DC motor drive circuit; S8. Analysis of power line conducted emission containment in brushless DC motor drive circuit; S9. Analysis of radiated emissions in brushless DC motor drive circuits.

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