What is the controller?
The siliXcon brushless motor controller, also known as an inverter, is an electronic device responsible for controlling electric motors. It operates as a 3-phase inverter that converts the direct current (DC) voltage from the battery into the alternating current (AC) voltage required by a 3-phase motor. The simplified schematic shown in the figure below illustrates this process. The voltage conversion is achieved by switching MOS-FETs in the power stage of the controller and connecting the motor's inductances to the positive or negative pole of the battery. The switching of MOS-FETs is modulated to generate a sinusoidal current (or any other desired waveform) in the motor's inductance.
It is important to note that only the currents flowing through the inductances exhibit a sinusoidal waveform. In contrast, the voltages connected to the inductances take the shape of high-frequency square pulses.
From an energy perspective, the controller functions as both an energy transformer and regulator. It converts the electrical energy from the battery, which consists of direct current (DC) voltage and current, into electrical energy suitable for the 3-phase motor, involving alternating currents (AC) and voltages. Furthermore, the controller controls the direction of energy flow, whether it is from the battery to the motor or vice versa. It is worth noting that the controller exhibits exceptional energy efficiency, reaching up to 98%, and possesses minimal energy storage capacity. As a result, a crucial conclusion can be drawn: the input power is equal to the output power.
This has at least three significant consequences:
While battery voltage is direct current (DC), motor phase voltage is alternating current (AC). Power calculations in AC and DC circuits vary, and the voltage values can also differ. Consequently, this implies that the current values may also vary.
Energy is accumulated in the motor through two different mechanisms. The first mechanism is the current flowing through the motor's inductance, and the second is the rotating mass of the rotor. The battery is the only safe storage space for this energy. When the battery is unplugged, there is no safe place to store the energy. The controller attempts to retain this energy within its DC link capacitor. However, the capacitor does not have sufficient capacity, resulting in a significant increase in voltage, which can lead to overvoltage and potential damage to the controller.
To power the motor controller - this point shares similarities with the previous one. Laboratory power supplies are generally not intended for energy absorption; they can only provide power. When the controller is instructed to brake the motor, it attempts to store energy in the laboratory power supply, which lacks the capability to absorb it. Consequently, this results in overvoltage and typically leads to damage to the controller and/or the power supply. This applies to all commonly used power supply types, not just laboratory power supplies.
Controller as VCU
The primary function of the motor controller has been described in the previous chapter. However, the controller also includes inputs and outputs to ensure its functionality. These interfaces can complement the primary function, allowing the controller to serve as the central vehicle control unit (VCU). User inputs are processed and evaluated directly by the controller, followed by the execution of the desired actions. This approach eliminates the need for an additional VCU unit and reduces overall costs.
For example, the figure below shows a system where the controller is the central VCU unit, and all the peripheries are connected.
