Sinewave vs Squarewave Controllers

One of the most vital components of an electric scooter or an electric bike is the controller.

The controller, also referred to as electronic speed controller (ESC), is essentially the brain of an e-scooter and functions to control virtually all aspects of the scooter. The controller links all electrical components of the e-scooter, including motor, battery, and throttle, hall sensors, etc., enabling each component to communicate optimally for the overall functioning of the scooter.

Electric scooter controllers (ESC) receive input signals from the various components of the scooter such as motor, battery, throttle, hall sensor, etc. With the help of firmware, the controller then analyses these signals and consequently implements appropriate action such as increasing or reducing the overall speed, turning off the motor to brake, and so much more.

In terms of phase voltage waveforms, electric scooter controllers are broadly categorized into sinewave and squarewave controllers. The difference is that sine waves have smoother transitions than square waves, which means they use less energy to get the same thing done. Sine waves oscillate in a smooth back and forth motion, while square waves oscillate in sharp angles at set intervals.

One predominant question among scooter riders is which one is better between the two types of controllers. But, it’s pretty challenging to pinpoint the better one considering that both have their fair share of benefits and downsides.

This post takes a detailed look at sinewave and squarewave controllers, looking at their functioning, differences, as well as pros and cons. Read on to find out more about sinewave and square electric scooter controllers.

What Are Electric Scooter Controllers?

In simple terms, an electric scooter controller is a miniature computer that acts as the brain of the e-scooter, controlling every function undertaken by the scooter. It links all the electric components in the scooter, including battery, throttle, motor, to a single place to facilitate optimum functionality. 

The primary role of an electric scooter is to receive all the inputs from all the electric components and then determine the necessary course of action. For example, when you twist or press the throttle, a signal is sent to the controller, increasing the amount of power from the battery to the electric motor. Increased power to the motor means faster propulsion of the wheels hence increased speed. 

In most modern scooters, controllers are integrated with a regenerative function where they recycle power when the regenerative brake is activated. They convert the kinetic energy harnessed from braking to electric energy, which is then channelled back from the motor to the battery for an even prolonged range. 

The controllers are usually fitted in a metallic rectangular sealed protective box in an electric scooter and mounted deep inside the frame or stem. The metallic enclosure is crucial to facilitate heat conduction, allowing the components of the controller to function optimally. 

Electric scooter controllers are broadly grouped based on functionality, motor type, ratings (current and voltage), and phase voltage waveforms. In terms of phase voltage waveforms, e-scooters can either be sinewave or squarewave controllers. 

Sinewave Controllers

Sine wave controllers produce sinusoidal waves which appear smooth and more formed. They are used with sinewave brushless DC (BLDC) motors with an approximately sinusoidal current and flux density distribution. The structure of a sinewave brushless DC motor is similar to that of a square BLDC motor, with surface-mounted permanent magnets on the rotor. This motor type achieves the required sinusoidal distribution of flux density by tapering the thickness of the permanent magnets towards the edges of the poles. 

A sine wave/ FOC controller (Failed Oriented Control) on a sinewave BLDC motor essentially functions as an inverter with a sinusoidal output current waveform. Usually, the inverter output phase is locked to the rotor position by controlling the inverter from a position transducer such as an encoder or a resolver. 

The rotor motion controls the inverter output frequency, as in the squarewave BLDC motor. The current phase is controlled such that the stator and rotor magnetic fields are at right angles.

How Do Sine Wave Controllers Work? 

Sine wave controllers function like (simulate) a simple on/off switch in a room or a dimmer switch, letting in power to the motor at particular instances. They form a smooth curve on their peak level and a smooth curve once they are back off. 

To understand the functioning of a sinewave controller, you need first to understand the makeup of brushless DC motors in electric scooters. A brushless DC motor on an electric scooter consists of permanent magnets on the rotor (the part which rotates) and electromagnetic coils on the stator (the stationary parts). These electromagnets are arranged in groups of three per phase- the reason brushless motors are often referred to as 3-phase motors. When you pass DC current through the coils, they become energised and transform into electromagnets. The operation of these motors is based on the simple force interaction between the electromagnets and the permanent magnet.

For the motor to revolve and consequently power up the wheels, the rotor and stator need to be energised and de-energised at different times. The stator electromagnets are arranged around the rim and energised differently. For instance, the stator electromagnets number 1, 4, 7, and 10 can be energised simultaneously, while the stator coils (electromagnets) 2, 5, 8, and 11 would be de-energised simultaneously. In the next phase, the stator coils number 1, 4, 7, and 10 would be de-energised simultaneously, while stator coils 2, 5, 8, and 11 would be energised at a go. 

The Field-Effect-Transistors (FETs) in the controllers are responsible for energising and de-energising the stator electromagnets, causing characteristic electric motor spins (motion). An FET essentially acts as a simple ON/OFF switch that energises and de-energises the stator electromagnets in an instance. An increase in the number of FETs in a controller means that the stator coils can be energised and de-energised concisely, enhancing its responsiveness.   

In essence, the sine wave controller rotates the motor rotor by constantly altering the voltage of the stator coil sinusoidally per the rotor’s rotation angle. The controllers are linked to sensors used to detect the position of the rotors every 60 degrees. The position of the rotor is estimated in real-time, and the controller releases a sinewave voltage based on the signal from the throttle. 

Properties of Sinusoidal Waves 

As mentioned earlier, sine wave controllers produce sinusoidal waves, which have various distinguishing properties, including:

• Sinusoidal signals are smoothly varying, i.e., they don’t have any sudden changes in amplitude. 
• In sinusoidal waves, also referred to as sine waves, the rate of amplitude changes is not constant, i.e., slope. The slope varies dynamically.
• Sine wave signals occur in repeated cycles. The number of cycles that occur in one second is equal to the frequency of the signal, usually abbreviated in hertz(Hz) 
• The amplitudes of sinusoidal signals often vary with respect to time. In some instances, degrees rather than time are used to describe the horizontal progression of the signal. Completing one full cycle equals 360°, and the halfway point happens at 180°.   

Benefits and Downside of SineWave Electric Scooter Controllers 

The most significant flex of sine wave electric scooter controllers is their enormous starting torque and outstanding scooter riding comfort. These controllers are also economical in terms of electricity and increase the torque at relatively low speed due to their high magnetic field torque utilisation at low speeds. Nonetheless, despite their benefits, sine wave electric scooter controllers bring about some downsides, as discussed below. 

Advantages of Sine Wave E-scooter Controllers 

• Sine wave controllers are usually dead-silent. They produce little noise facilitating a comfortable scooter riding experience. This is because they make pure sine waves, which have very low harmonic distortion causing the electric scooter to run quieter. 
• Sine wave controllers deliver enormous starting torque producing faster scooter starting acceleration. 
• In normal riding conditions, a sine wave e-scooter can achieve constant speed movement, better known as cruise speed, with outstanding ride comfort the whole way. 
• A sine wave controller has a higher motor efficiency when climbing steep inclines or when carrying heavy loads. 
• Sine wave e-scooter controllers have more efficient and predictable control of all operations than their counterparts. They prevent crashes or glitches in the scooter components, which could cause serious malfunctions.
• Sine wave e-scooter controllers are more efficient in terms of electricity consumption, thus offering greater range and prolonging battery life. 

Disadvantages of Sine Wave E-scooter Controllers 

• Highly-priced 
• Only compatible with matched motors 

Square Wave Controllers

Square wave controllers produce trapezoidal waves, which are rather juggled, not smooth. The transitions between each square wave cause harmonic losses (loss of energy through sound in square wave controllers), making them less efficient. These controllers also have minimal computational power needs, requiring only the 3 phase on/off signal to drive the motor in a time sequence.

Compared to sinewave controllers, square wave controllers are generally cheaper due to minimal computational power needs.

Properties of Square Waves

A square wave is best described as a non-sinusoidal periodic waveform where the amplitude alternates at a steady frequency between fixed maximum and minimum values. The time between the minimum and maximum durations is almost similar. In a perfect square waveform, the maximum and minimum transitions are instantaneous. However, a perfect square wave is practically impossible to create, considering that the falling and rising edges are never instantaneous, plus the tops are never flat. A practical square wave(trapezoidal wave) usually has a non-zero rise time, and the tops are rarely flat.

Unlike sine waves with a smooth ascending and descending waveform with rounded edges at the negative and positive peaks, square waves have pretty steep, almost vertical negative and positive peaks. The top and bottom of the waveforms are usually flat, producing a waveform that matches its description, i.e., square.

Some properties of square waveforms include: 

• Square waveforms have instantaneous transitions between the negative and positive peaks. But this is rarely achieved in practice owing to the physical limitations of the controllers. The rise time and fall time refer to the period taken for the system to rise from the high peak and low peak, respectively.
• In some cases, square waveforms never reach the theoretical low and high level, usually due to system overdamping or under damping. It will only oscillate about the high and low levels before settling into an intermediate level.
• The positive portion equals the negative amount in one cycle (one up and down portion). The cycle repeats itself dozens of times, corresponding to the transmitted signal.

Benefits and Downside of Square Wave Electric Scooter Controllers

The most significant benefit of electric scooter controllers is that they are more affordable than sine wave e-scooter controllers and are compatible with different motors, including geared and gearless motors. What’s more, they offer more efficiency in times of sudden acceleration and braking. However, square wave electric scooter controllers produce a great deal of noise when in operation and offer punchy, nonlinear control. 

Pros of Square Wave Electric Scooter Controllers 

• Square wave electric scooter controllers are more affordable compared to their counterparts (sine wave e-scooter controllers) thanks to their minimal computational power need. 
• There’s no need to undertake motor matching or tuning with a square wave controller since they are compatible with a wide range of motors, including geared and gearless motors. 
• Square wave controllers produce more torque than their counterparts, creating a punchy acceleration.
• Square wave controllers are great performers in braking and sudden acceleration.

Cons of Square Wave Electric Scooter Controllers 

• Unlike their counterparts, square wave controller motors produce louder noise and heat, especially at average speeds. This makes them less efficient. 
• These controllers deliver nonlinear punchy acceleration. The overall acceleration of the scooter may be jerky, compromising the overall comfort. 
• Square wave controllers have lower efficiency in handling heavy loads and climbing steep roads. 
• With squarewave controllers, a voltage surge at high speed or acceleration may result in overheating and, even worse, damage to the vital components in the scooter, causing its complete shutdown. 

Sinewave vs Squarewave controllers

BIO: 

Nely is an adrenaline junkie and one of her life goals is to sky dive, but until that day she gets her kicks from testing fast electric scooters. Part time scooter fanatic & part time SEO analyst. Nely’s favourite scooter is the Dualtron X.