Field-oriented control drive circuit design

Field-oriented control drive circuits, as a new type of control method recently, are different from the traditional control principle of electronic speed controllers and have gradually started to be used in large numbers in recent years. The correct design of the circuit and the implementation of the algorithm to realize precise control of the brushless motor is a question worth investigating. The research purpose of this paper is to design a field-oriented drive circuit to drive a brushless motor with the smallest possible size and the largest possible load to improve performance and usability. Based on the current design of the field-oriented control drive circuits, the author has selected the right microprogrammed control Unit and algorithm to improve the practicality and performance of the field-oriented control drive circuits. Finally, a few advantages of this field-oriented control drive circuits are summarized. The conclusion of this research is that the brushless motor can be controlled precisely by a simple operation. However, the cost is that the algorithm design is more complicated.


Introduction
Electronically controlled speed regulator has characteristics of sensitive action, good stability.It has a great degree of improvement in the hole speed accuracy, dynamic response, speed control mode flexibility and adaptability [1].The FOC control differs from the control principle of an electronic governor.FOC (Field-Oriented Control), also known as Vector Control (VC), is one of the best methods for efficient control of brushless DC motors (BLDC) and permanent magnet synchronous motors (PMSM).Compared with traditional square wave control, vector control technology can greatly improve the smoothness of motor torque and meet the requirements of high precision, fast and stable operation [2].The basic principle of Field-Oriented Control is to adjust the stator current component field current and torque current respectively by feedback and control torque under the specified Angle of synchronous rotation coordinate system [3].The research purpose of this paper is to Improve the performance and practicality of the drive circuit by designing the FOC control circuit and selecting the control unit that implements the FOC algorithm.The research first displays the control flow chart of Field-Oriented Control, then introduces the algorithms and displays the circuit, and refers to the microprogrammed control Units used in the research.Finally is the use of microprogramming control units and the implementation of FOC algorithms.

Literature review
The control of permanent magnet synchronous motors often employs commonly used control methods such as constant voltage-frequency ratio control, field-oriented control (FOC), and direct torque control.Among these methods, FOC stands out due to its numerous advantages including high power density, high torque density, minimal torque pulsation, superior controllability, and stable frequency conversion speed regulation.These characteristics make FOC highly suitable for practical motor applications.As a result, FOC is extensively utilized in the control of permanent magnet synchronous motors, meeting the specific requirements of such systems [4].Recent years, Algorithm and control strategy has some Improvements, researchers are constantly improving FOC algorithms and control strategies to improve motor performance and efficiency.For example, some research has focused on developing more accurate current control algorithms to reduce torque and speed errors.In addition, some improved control strategies take into account motor nonlinearity, saturation and parameter uncertainty, which improves the stability of the FOC system.The paper has introduced some algorithms and control strategies for Field-oriented control drive circuits, which allows a smaller board drives a motor with more torque and allows more precise control of the motor's rotation at a manageable cost.

FOC drive circuit design
The basic means of driving a brush-less motor with FOC is to calculate the required voltage vector and generate a commissioning signal using the SVPWM space vector pulse width modulation technique to drive a three-phase inverter circuit, which synthesizes an equivalent three-phase sinusoidal voltage to drive the motor.The SPWM is based on PWM and is modulated by a sine wave to produce a square wave with a sine wave pattern.However, SPWM debugging is not commonly used.The reason for this is that SPWM has a lower bus voltage utilization than SVPWM.
FOC control flow chart: Figure 1.FOC control flow chart.As shown in Figure 1, the FOC control flow for a three-phase motor involves several steps.First, the motor current is sampled.Then, a variable to be controlled is reduced using the Clark transform, followed by obtaining two constants for control using the Park transform.The error between the sampled value and the set value is then calculated and fed into a PID controller to obtain the output control voltage.Next, the Park transformation is inverted to synthesize a voltage space vector, which is used to generate a real-time inverter bridge state code via the SVPWM module.The MOS tube is then switched according to the coded value to drive the motor.Finally, this cycle repeats to ensure continuous control.
Three-phase inverter circuit: By controlling the switching state of the MOS tubes of the bridge circuit, an equivalent sinusoidal wave is generated to stabilize the drive motor.The structure of the three-phase bridge inverter is shown in Figure 2. The inverter has a three-phase bridge arm, and a pair of switching components exist on each phase, which adopts the star connection mode [4].

Clark Transformation:
The main purpose of using the Clark transform in FOC drive circuits is to convert the three-phase AC signal into a vector form in a right-angle coordinate system to facilitate magnetic field rotation and vector control.The FOC drive circuit needs to control two parameters of the motor: the magnetic field strength and the speed.To control these two parameters, the current and voltage in each phase need to be calculated and adjusted in real-time in the FOC controller so that the actual motor motion is consistent with the desired state.
The Clark transform converts the three-phase AC signal into two independent signals, the d-axis (flux direction) and the q-axis (rotor direction), so that the magnetic field rotation and speed can be controlled by simple vector operations, thus controlling the motor's motion.At the same time, the use of the Clark Transform facilitates the control of the motor current and voltage to ensure stability and efficiency during motor operation.The use of the Clark Transform is therefore an essential part of the FOC drive circuit.
The following are the specific steps of the Clark Transform: The three-phase AC signal is arranged 120 degrees apart to form a complex vector a.This vector a is rotated by 45 degrees to obtain a new vector b, so that the vertical line of the vector b coincides with a.This rotation is usually denoted θ.
The projection of vector b in the direction of the d-axis is the component Id in the flux direction and the projection in the direction of the q-axis is the component Iq in the rotor direction.This gives a vector in the d-q right-angle coordinate system, which is the vector in the scalar system, which represents the equivalent of the original three-phase vector.
The Clark transform can be expressed in the following matrix form: This matrix A transforms the three-phase voltage or current vector a into the equivalent vector b in the Cartesian coordinate system, i.e. b = Aa.
The Clark transformation converts the three-phase AC signal into two-dimensional coordinates in the right-angle coordinate system, facilitating vector control.By controlling and adjusting the two components in the d-q coordinate system, precise control of the magnetic field rotation and motor speed in the FOC drive circuit can be achieved.

Park transform:
The synchronous generator is transformed from a, b, c stationary coordinate system to d, q, o rotating coordinate system during operation [5].After the Clark transformation, the three-phase AC signal has been converted into a vector form in the right-angle coordinate system, and two components are obtained, i.e., the vector components on the d-and q-axes.However, these two components are actually related to the position of the rotor.In the FOC controller, the vector control of the motor requires the conversion of these rotor position-dependent components into rotor-independent vector components in the stationary coordinate system (ds,qs), which is where the Park transformation comes into play.
To implement FOC control, the Clark transformation is used to convert the three-phase AC signal to the d-q right-angle coordinate system, and then the Park transformation matrix P is calculated based on the current rotor position to transform the vector b to vector c, where the first component ds represents magnetic flux in the rotor rest coordinate system and the second component qs represents rotational speed in the rotor rest coordinate system in the stationary coordinate system (ds-qs).This makes it easy to control parameters such as the motor's magnetic field and speed to improve the efficiency and accuracy of the motor drive.
As shown in Figure 4, PWM generates an equivalent sine wave:

Spatial voltage vector synthesis diagram:
Compared with the early use of sine-wave equivalent pulse width modulation (SPWM) method, SVPWM can overcome the SPWM voltage utilization low, high power consumption, heat generation, high harmonic current and other problems.For motor regulation, SVPWM can often achieve a short adjustment time, a small overshoot, a small steady state error, and a high voltage utilization [6].
The two components obtained after the inverse Park transformation are usually called vectors.With the SVPWM technique, it is possible to generate six space voltage vectors using these two vectors.These two vectors can be used to generate six spatial voltage vectors.
To see how these vectors can be mapped into space, consider choosing a sine wave as a reference point in a three-phase AC system.Then represent the three-phase voltage signal as a set of elementary vectors arranged in space at 60 degree intervals in a hexagon.As shown in Figure 5, using the SVPWM technique, vectors can be mapped into the space vector map according to their direction and magnitude.Specifically, two parameters need to be determined in order to generate the required output voltage vector: the duty cycle and the vector direction.The duty cycle controls the width of the output (PWM) signal, while the vector direction is used to select the appropriate vector.As shown in Figure 6 to Figure11, the circuit schematic and circuit PCB are as follows: In figure 6, TPS54331 is a high-efficiency, low-cost synchronous boost converter introduced by Texas Instruments.It is widely used in portable electronic devices, communication equipment, industrial systems, and automotive electronics.The converter features advanced constant-frequency current mode control, achieving up to 96% efficiency and minimizing power consumption.It has a wide input voltage range of 4.5V to 28V, adjustable output voltage, and built-in protection functions for system reliability.With small package options, it enables compact power supply designs in limited space.TPS54331 offers flexibility with adjustable frequency, soft start, and low-noise operation modes, making it suitable for various power supply needs.Overall, it is an efficient and flexible boost converter solution with integrated protection features, ideal for compact and efficient power systems in

Microprogrammed control Units used INA240:
The INA240 is a cutting-edge current-sensing amplifier that incorporates advanced PWM suppression technology to deliver superior performance in applications that employ pulse-width modulated signals.By detecting the voltage drop across the shunt resistor, this voltage-output device can accurately measure current over a wide range of common-mode voltages (-4V to 80V) independently of the power supply voltage.Its unique negative common-mode voltage feature allows it to operate seamlessly below ground voltage, which is particularly useful in solenoid applications.With its exceptional PWM suppression capability, the INA240 can effectively minimize the impact of large common-mode transients (ΔV/Δt) that are commonly found in motor drives and solenoid control systems.This enables the device to provide highly precise current measurements with minimal output voltage transients and recovery times ripple [7].

TPS54331:
The TPS54331 component is a non-synchronous buck converter rated for 28V and 3A, featuring an integrated high-side MOSFET with low RDS(on).Notably, the device incorporates a pulse-hopping Eco-mode mechanism that operates automatically to enhance efficiency during periods of light load [8].

L6234:
The L6234 is a triple half-bridge circuit designed for the purpose of driving a Brushless DC motor.It has been implemented using the BCD multi-power technology, which seamlessly integrates isolated DMOS power transistors with CMOS and Bipolar circuits within a single microprogrammed control unit.The utilization of mixed technology has facilitated the optimization of both the logic circuitry and the power stage, leading to the attainment of unparalleled performance levels [9].

AMS1117:
The AMS1117 represents a range of voltage regulators characterized by their low dropout, capable of delivering an output current of up to 1A.The product line is composed of six distinct, pre-determined voltage levels, specifically 1.2V, 1.5V, 1.8V, 2.5V, 3.3V, and 5.0V, as well as an adjustable version.The reference/output voltage is subject to on-chip precision trimming, allowing for an accuracy level within ±2%.Furthermore, the device includes on-chip thermal limiting, a feature designed to safeguard against any combination of overload and ambient temperatures that may lead to excessive junction temperatures [10].
The Field Oriented Control (FOC) system consists of several key components.The first is the motor itself, which can be a DC or AC motor and is the most fundamental part of the FOC system.The second component is sensors, which include Hall sensors, encoders, and other measuring devices to monitor the motor's position, speed, current, and other status parameters, and provide feedback to the FOC controller.The third component is the power supply circuit, which is responsible for providing stable DC or AC voltage or current to the controller to ensure the normal operation of the FOC system.The fourth component is the FOC controller, which implements the FOC algorithm and contains several functional modules, including Park/Inverse Park Transformation, Clark Transformation, PID controller, and more.Finally, the fifth component is the drive circuit, which converts the current/voltage signal from the FOC controller into a suitable drive signal for the motor and connects it to the input of the motor via the interface board.Together, these components enable the FOC system to achieve precise control of the motor's speed, torque, and other parameters.

Advantages of the designed circuit
FOC controllers have several advantages over brushless ESCs.Firstly, due to the difference in control principles, brushless ESCs can only control the motor at high speeds and are difficult to control at low speeds.In contrast, FOC controllers do not have this limitation and can achieve precise control regardless of speed.Additionally, the FOC controller can also be used as an energy recovery brake, adding to its versatility.Moreover, FOC drives are much quieter than ESCs because ordinary ESCs are driven by a square wave, whereas FOCs are driven by a sine wave.Finally, FOC drives possess several other advantages such as high power, high torque, small size, and lower cost.

Conclusion
The FOC control circuit enables motors with higher torque to be driven by a smaller board size and allows more precise and cost-controlled control of motor rotation.From the use of the microprogrammed control Unit to the micro-control unit that implements the FOC algorithm, reflecting an improvement in the parameters of the control circuit.However, FOC circuits also have some shortcomings, mainly including the following aspects: high cost, requiring complex hardware design and high-performance processors; slow response speed, requiring calculation and therefore relatively slow response; and difficult debugging, requiring fine parameter settings and high technical proficiency from engineers.In the future, research on FOC circuits may focus on reducing costs by using more advanced processors and design technologies, improving response speed by focusing on computing speed and algorithm optimization, and simplifying debugging through the development of more intelligent and automated debugging tools.

Figure 2 .
Figure 2. Three-phase inverter circuit.As shown in Figure 3, Three-phase sine AC waveform diagram is displayed as follow:

Figure 3 .
Figure 3. Three-phase sine AC waveform.Clark Transformation:The main purpose of using the Clark transform in FOC drive circuits is to convert the three-phase AC signal into a vector form in a right-angle coordinate system to facilitate magnetic field rotation and vector control.The FOC drive circuit needs to control two parameters of the motor: the magnetic field strength and the speed.To control these two parameters, the current and voltage in each phase need to be calculated and adjusted in real-time in the FOC controller so that the actual motor motion is consistent with the desired state.The Clark transform converts the three-phase AC signal into two independent signals, the d-axis (flux direction) and the q-axis (rotor direction), so that the magnetic field rotation and speed can be controlled by simple vector operations, thus controlling the motor's motion.At the same time, the use of the Clark Transform facilitates the control of the motor current and voltage to ensure stability and efficiency during motor operation.The use of the Clark Transform is therefore an essential part of the FOC drive circuit.The following are the specific steps of the Clark Transform: The three-phase AC signal is arranged 120 degrees apart to form a complex vector a.This vector a is rotated by 45 degrees to obtain a new vector b, so that the vertical line of the vector b coincides with a.This rotation is usually denoted θ.

Figure 5 .
Figure 5. Space vector map.As shown in Figure6to Figure11, the circuit schematic and circuit PCB are as follows: In figure6, TPS54331 is a high-efficiency, low-cost synchronous boost converter introduced by Texas Instruments.It is widely used in portable electronic devices, communication equipment, industrial systems, and automotive electronics.The converter features advanced constant-frequency current mode control, achieving up to 96% efficiency and minimizing power consumption.It has a wide input voltage range of 4.5V to 28V, adjustable output voltage, and built-in protection functions for system reliability.With small package options, it enables compact power supply designs in limited space.TPS54331 offers flexibility with adjustable frequency, soft start, and low-noise operation modes, making it suitable for various power supply needs.Overall, it is an efficient and flexible boost converter solution with integrated protection features, ideal for compact and efficient power systems in

Figure 6 .
Figure 6.Schematic circuit.AMS1117-3.3 is a linear regulator commonly used to stabilize higher input voltages to a fixed 3.3 volts output voltage.It is an integrated circuit manufactured by Advanced Monolithic Systems (AMS).The main features and functions of the AMS1117-3.3regulator include a fixed output voltage of 3.3 volts, making it suitable for powering low-voltage systems and components in electronic devices.It accepts a wide input voltage range, typically ranging from 4.75V to 12V, providing flexibility to meet different power supply requirements in various applications.The AMS1117-3.3 offers low output noise, excellent output voltage stability, and low dropout voltage, which are crucial for applications that demand a stable and clean power supply.It includes internal protection circuits for overheat and overcurrent protection, safeguarding the regulator and other circuits from potential damages caused by input overvoltage or short circuits.When using the AMS1117-3.3,only a few external components such as input and output filtering capacitors and bypass capacitors are typically required to achieve stable and reliable output.It provides multiple packaging options, including SOT-223, SOT-89, and TO-252, catering to different installation methods and space constraints.